What went wrong before?

Since 1960 there have been at least ten studies or attempts to build a southern rail access to Heathrow.

By the 1990s the scheme became known as Airtrack, and the name was retained by subsequent schemes, all of which have been rejected by local planning authorities.

BAA, the former owner of Heathrow, proposed Heathrow Airtrack, which would have run services through the airport to Waterloo, Guildford and Reading. The idea was dropped in 2011, with lack of Government subsidy cited as a key obstacle.

Local councils revised the scheme, calling it Airtrack Lite and using a section of the former West Drayton to Staines railway line running parallel to the M25 (as in the latest Heathrow Southern scheme).

It would have required only 2½ miles of new track (much less than the eight miles proposed by Heathrow Southern), and would have run from a tunnel beneath Heathrow across Stanwell Moor and Staines Moor, with new track into Staines town centre to a remodelled Staines station, as well as a new depot at Feltham.

It envisaged two trains an hour to Waterloo, two to Guildford via Woking, and two to Reading.

The key issue was the large number of level crossings - 15 on the whole route. Local Runnymede and Weybridge MP Philip Hammond, later Secretary of State for Transport and now Chancellor of the Exchequer, raised serious concerns about the impact on Egham level crossing, which would have been closed for up to 40 minutes each hour.

He was involved in a petition to the then Labour Government not to allow Airtrack because of the impact on his constituents. Concerns about level crossing closure times were also raised by local authorities, business groups and emergency services.