Forty years ago, a world first occurred, as the first ever underground rail link between an airport and a city opened, as the London Underground arrived at Heathrow Airport.

The link brought the Piccadilly line into the heart of Heathrow with the opening of a new tube station – Heathrow Central, and it marked the completion of a staged opening of the extension of the tube line.

That was all 40 years ago today, but it was not an easy railway to build.

The Piccadilly line had reached Hounslow West in 1933 (which it shared with the District line), where it remained a terminus until the 1970s. By now Heathrow Airport was handling around 20 million passengers per year, and something needed to be done to fix a flaw in the airport design.

When it was originally decided to put the terminal buildings as a cluster in the middle of the airport, it was felt that as air travel was so expensive, the passengers would arrive by chauffeur driven car, so there was no need for mass transport facilities, such as bus or car parks, or a rail link.

As passenger numbers rose, this became a serious issue, and as a compromise, fleets of coaches carried people between the city and airport, with British European Airways (BEA) having its West London Air Terminal in Kensington connecting to the airport by bus with a trailer for the luggage.

However, pressure was increasing to connect Heathrow by railway to central London.

We want trains!

A rail link was needed, but the idea of extending the London Underground to Heathrow wasn’t necessarily the first choice.

A rail link to the airport was being talked about as far back as October 1946, when a government committee was set up to look into the matter. Over the subsequent years, a number of committees were set up, investigated things, and closed without anything being done.

In 1956, the government ruled in favour of a mainline railway, saying that trips by tube would be too slow. But still nothing was done.

However, there were developments on the other side of the Atlantic, as the Jumbo Jet was under development, and the era of relatively affordable air travel was about to arrive. Heathrow was in the middle of a massive upgrade to handle the giant planes, and was increasingly worried about how to handle the huge surge in passengers.

Finally, phew, in 1967 the Heathrow Link Steering Group, under the aegis of the Ministry of Transport was to be successful. Initially though they supported a mainline rail link.

The rail link was proposed by British Railways, offering 8 trains per hour over existing mainline tracks to Victoria and Waterloo. This was widely considered to be unlikely as the mainline services were already pushing the limits of what they could carry.

A mainline link was also not expected to be opened before 1975, whereas the London Transport Board had indicated that it was ready to extend the Piccadilly line “at short notice”, and could open a service in 1973.

Plans for a monorail didn’t get very far.

London Underground not to be diverted by such irritants as a government committee disagreeing with it, increased lobbying for their tube train link. They set up a bus link from Hounslow West to the airport, to show that the tube would be able to handle air traffic passenger luggage and the like.

Heathrow preferred the mainline railway, as much of the check-in facilities could be added in Central London, while BEA preferred the tube, seeing it as less competition for its own bus service.

The tube offer was cheaper than the mainline, would be better for local workers, but would be slower for airport passengers. In the end the numbers came down in favour of London Underground, boosted by the local area benefits, and support from the GLC.

Finally, in December 1970, the £15 million tube line proposal was approved, and the GLC offered a 25% grant towards the cost of the extension, but nothing (at the time) from the government, although they eventually also stumped up a quarter of the cost.

Not that everyone was happy, as Hugh Jenkins MP for Putney lambasted the waste of money as he said that imminent plans for a replacement airport by the Thames Estuary would render Heathrow redundant. That worked out well then.

This fairly short extension of the Piccadilly line toward Heathrow was however to prove unexpectedly difficult to build.

Construction Starts

The first decision was what sort of tunnel to dig. What we have is a tunnel dug just under the surface from Hounslow to the edge of the airport, where it dives down into a tube tunnel.

As the Victorians had found, digging a shallow railway tunnel by the cut-and-cover method is very disruptive to people in the area, hence most tube tunnels are bored deep below street level.

However, to drill a deep tunnel along the entire length would have meant a slope starting much further east than planned, near Houslow Central. It would also also meant longer escalators and lifts at the two intermediate stations.

A further consideration was that cut-and-cover work did not require specialist tunnel labour which is often in short supply. This was quite important as the cut-and-cover works coincided with the Fleet Line tunnelling works.

The cut-and-cover option was also about 10% cheaper the full tube tunnel proposal, although as we are to see maybe that was an unwise attempt at cost savings.

The first ceremonial sod of earth was cut on 28th April 1971, although it’s said that the airport, still smarting from losing its mainline railway insisted on the soil being put back once the VIPs and media had left.

One of the first things that had to be done to prepare the land for the railway was get rid of everything else that was in the way – sewers, telephone cables and the like. No fewer than ten statutory authorities had to move their equipment and at times all of them were on the site at once.

All this before the proper tunneling could even start.

As the Piccadilly line faced southwards at the existing Hounslow West station — in the wrong direction, a brand new station was needed. This was constructed as a basic box in the ground then filled in with the fixtures and fittings to turn it into a station.

They retained the original surface building, by the Underground’s architect Stanley Heaps in conjunction with Charles Holden, and linked the new platforms to the old station via a covered footpath.

From here, a run of cut-and-cover tunnels were dug pretty much following the main road, up the Bath Road, then along the side of the Great South-West Road down to Hatton Cross. A direct line between the stations would have been quicker, but it would have run under housing.

For the cut-and-cover tunnels, secant piles were driven down into the ground to form an outer wall, then the soil removed from the center and a roof laid on top.

Within the tunnels, where they run close to residential or commercial properties, special vibration damping track had to be laid.

The cut-and-cover tunnel largely runs about a metre below the surface, but at one point it ducks deeper to avoid a major sewer, and more famously, it runs up to the surface for a few seconds to leap over the River Crane.

The tunelling eventually reached the lost village of Hatton, now remembered in the tube station at the location, Hatton Cross. This was to prove to be a surprisingly difficult station to build, considering that it’s just a shallow box in the ground.

The main problem was a 9 metre height limit imposed by the planes approaching the airport, and that pilling rigs tended to be talled than that. A rethink and a more expensive method of constructing the walls was used, and even that needed specially modified equipment to stay within the height restrictions.

Unsurprisingly, a lot of time was lost, and also thanks to the somewhat experimental nature of the diaphragm walls, a lot of corrective action needed to repair badly piled sections. Even extracting the soil proved more difficult than planned due to fumes from the Traxcavator and they had to remove some of the roof beams to let in fresh air.

Due to the delays in construction, the track laying was done using precast slabs to try and reclaim some lost time

Eventually though, Hatton Cross and the new Hounslow West stations opened on 19th July 1975, with Hatton Cross as a temporary terminus station as it is on the southern border of the airport.

The large, indeed too large and heavy building design for the station is often claimed to be due to a need to survive an impact from an airplane crash. Actually, it’s simply that London Underground had planned to build offices on top of the station to rent out, so the foundations and ground floor had to be built to support the office block, but they’ve never got around to finishing it.

Meanwhile, a new type of tunnelling was in action to finish the final section right into the heart of Heathrow Airport.

The final push

Although Heathrow is largely built on marshy land, that’s on the surface, for deeper down is very nice to tunnel through clay, and as trains leave Hatton Cross they dive sharply down to reach the clay level where tunnelling was easiest.

This was still the era of hand tunnelling – no sign yet of the massive tunnel boring machines, so while mechanical equipment could cut away at the tunnel face, the rings and the protective shield were still installed by hand.

Most of the tunnel is lined with concrete rings, but in places, they used left-over rings from the recently completed Victoria line tunnels in central London. In fact the entire tunnel was intended to be made from metal rings, but they found concrete tunnel linings to be cheaper to manufacture.

Although they were tunnelling deep under the airport, access shafts were dug down to them, still in use for ventilation, and the equipment used suffered from an even tighter height restriction caused by the control tower’s radar needing to have a clear sight of the southern runways.

A large cross-over tunnel also had to be constructed just outside the new station to allow trains to use either platform. Due to the larger tunnel being dug in water bearing gravel instead of clay, the works were done in a sealed site with compressed air to prevent water flooding into the tunnels.

The tunnels run past the station into overrun tunnels that were designed to point towards Perry Oaks, one of the lost villages under Heathrow’s runways in case an extension was needed. Perry Oaks is now Terminal 5, so forward planning worked, albeit with a considerable delay.

While the tunneling went on, the construction of the new tube station in the centre of Heathrow Airport was underway.

This was a mix, of a deep box for the ticket hall, and then escalators down to the platforms which were dug out by hand around the tube tunnels which had already been completed at this level some 17 metres below ground.

When you dig a very large deep box in the ground, taking all that heavy soil out can result in hydrostatic forces from the waterlogged soil causing the station floor to buckle upwards before the rest of the station building is added into keep it flat. So they had to add a special rubble drain to prevent that happening.

There was also a shortage of steel during construction which caused delays to the station works.

There had been plans to allow for a British Rail service in the future as well, but it was decided that both the cost and the technical complexity didn’t merit it. Today the Heathrow Express tunnels and platforms are a hundred yards away from the tube tunnels.

Although expected to open in 1976, thanks to strikes, a 3-day week in 1974, equipment shortages and the design changes, by October 1975, London Transport was pushing the expected opening to the latter half of 1977

The cost had also spiraled to £30 million by now.

Finally though, at 11:30am on the 16th December 1977, history was made when Heathrow Central was opened, by The Queen, and created the world’s first underground rail link from an airport.

There was a worry though, a strike by lift and escalator engineers meant that the Queen might have had to walk up the stairs, but in the end regal disaster was narrowly averted, and the escalators fine worked on the day.

The Queen and VIPs wandered off with their commemorative train tickets, and paying passengers were allowed to follow, using normal tickets, with the first public train leaving Heathrow Central at 3pm.

The opening of the line also marked the arrival of one of London Underground’s most iconic posters, and one of your correspondent’s personal favourites.

So happy birthday to 40 years of flying the tube.


Flight International, 8th May 1969

Flight International, 31st July 1969

Heathrow: From Tents to Terminal 5 by Ian Anderson

The Times, 22nd May 1970

The Times, 7th Nov 1970;

The Times, 22nd Oct 1975

Extension of the Piccadilly line from Hounslow West to Heathrow – Proceedings of the Institution of Civil Engineers 1976

Rails through the Clay by Alan Jackson and Desmond Croome


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  1. Bio Bopp says:

    Disappointed to see HM standing on the left in that video.

  2. Andrew says:

    Terrific capture of some history, as the city of nearly 5 million people where I live can’t get its act together and build an airport rail link. Thanks.

  3. Melvyn says:

    Given the District Line use daily to with the Piccadilly Line to Hounslow West then I always thought that extension of the District Line with its bigger trains and stations nearer the surface in Central London would have been a better option.

    However, given the method of construction and space limits along the route then a sub surface sized line might not have been possible.

    I am surprised that given Hatton Cross Station can sometimes be the terminal if problems arise at the Heathrow Stations that this station still doesn’t have lift access given needs of passengers with luggage to get from and to the trains .

    While the alternative route by rail to Heathrow still remains a bus link from Feltham Station with one reason given for not building this extension being the number of level crossings on South West Rail route !

  4. Gary Narborough says:

    I found this very informative article quite by chance and enjoyed very much thank you. Some very illuminating history.

  5. Philip Brown says:

    This is an outstanding long read Ian, and a very enjoyable history of the politics, engineering and public administration of a pioneering infrastructure project which I found both very enjoyable and very informative to read. May I however question if it was indeed “the first every underground rail link between an airport and a city” as Boston’s Blue Line of the MBTA was opened to Logan Airport in the early 1950s. While I’m aware that the station at Logan Airport is on the surface, far more of the rail link itself from Boston to Logan is underground than the rail link of the Picadilly Line from London to Heathrow, particularly through zones 2-5! If however you do mean the airport station itself being underground, I’m sure you are correct in this assertation.

    Thanks again for a brilliant piece of writing – I look forward to reading more of them in the future!

  6. Uchenna says:

    This was a very enjoyable read! But unfortunately, Clevland’s Red line beat the Piccadilly line as the world’s first underground airport rail link. But I love the underground and I’m currently learning more about it.

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