AN international rail interchange could be built at Heathrow to compensate for the environmental harm caused by a new third runway at the airport, the transport minister Lord Adonis has indicated.

In an interview with The Sunday Times, Adonis said the government was enthusiastic about proposals for a £4.5 billion station called the Heathrow hub, which could slash more than two hours off train journeys from some British cities to European destinations.

Supporters of the scheme say it would extend the high-speed European rail network, which currently stops at London, north to benefit the rest of Britain.

The hub, which would be the country’s largest railway station, was first proposed as an alternative to the third runway by the Tories, who argued that the extra capacity needed at Heathrow could be shifted on to rail rather than air.

Now, in a surprise move, the government appears ready to embrace both projects. It could use the new railway station’s environmental credentials as a “sweetener” for giving a polluting third runway the go-ahead.

It would enable far more passengers to travel by train rather than car to the airport and enable some to ditch the plane altogether for travelling to Europe.

Adonis said: “I think that it’s an attractive idea. It’s vital that we have an integrated approach to planning new rail capacity and any new airport capacity that’s also required.”

The Heathrow hub would link a new high-speed London-Scotland railway line to cities on the continent.

Adonis said: “The key issue on the hub is whether the north-south line would also serve Heathrow and therefore offer much better interchange facilities at Heathrow and the capacity to get to and from Heathrow much more rapidly and conveniently from other parts of the country.”

In a strong hint that all three projects — the 200mph north-south line, the Heathrow hub, and a third runway – could be developed together, he said: “It makes good sense to plan improvements to Heathrow and the rail system together.”

Cities that could benefit most include Birmingham, from where passengers could reach Paris by train 2hr 45min more quickly than now, and Manchester, where the saving would be even more.

The disclosure that ministers are seriously considering the hub comes as Downing Street issued its strongest hint yet that it would give the go-ahead to the third runway.

A spokesman highlighted “a decision” on the scheme as an example of how the government is “making investment in transport to ensure our infra-structure is fit for the needs of the 21st century”.

Adonis refused to be drawn on the decision, but brushed off evidence that Labour could lose marginal seats in the flight-path area if the third runway gets the go-ahead. Indicating that Labour is ready to “take the hit” in constituencies opposed to the project, Adonis said the decision would have to be “based on legal and transport implications”.

Boris Johnson, the London mayor, has announced, however, that he will hold a last-minute public debate on the runway plan on January 21 at which opponents will make a final effort to press their case.

Plans for the hub, drawn up by Arup, the engineering consultancy, have already been presented to the Department for Transport. They envisage a 12-platform station built on the northern boundary of Heathrow, operating direct high-speed services to the continent and cities such as Leeds, Manchester and Bristol.

Existing lines, such as the Great Western main line from London to Bristol, would be diverted through the station, providing direct connections to the airport from the west, southwest, Wales and the Midlands. The hub would be linked around London to the existing Eurostar line.

However, Theresa Villiers, the shadow transport secretary, said: “A new rail hub at Heathrow should be an alternative to a third runway not a sweetener for it.”

Adonis also said in his interview that the government was considering a new network of stations along key routes, designed to encourage drivers to switch part of their journey to rail.

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