Hounslow MPs Ann and Alan Keen have been accused of “betraying” their constituents by voting in favour of a third runway at Heathrow - revealing a dramatic shift in their stance on expansion.

Ann Keen, MP for Brentford and Isleworth, and her husband Alan, MP for Feltham and Heston, have previously insisted they had been opposed to Heathrow expansion for many years, but both appeared to bow to Government pressure during a House of Commons debate yesterday.

Campaign groups slammed the couple over their decision.

Nic Ferriday, of West London Friends of the Earth, described their actions as “contemptible,” adding: “Ann Keen's performance was particularly irksome. Having come out publicly and strongly against Heathrow, she has now betrayed her constituents and the people of west London.

“As a health minister, her indifference to more air pollution, which already kills a thousand Londoners a year, is reprehensible."

The debate and vote, which was not binding, was called by the Conservatives and saw the biggest rebellion on an opposition motion since Labour came to power in 1997. The Government won by 19 votes.

Health Minister Mrs Keen did not speak in the debate, but her husband - who was one of 57 MPs who signed an Early Day Motion last year against a third runway - told the House of Commons he would vote against the Conservatives’ motion, despite his opposition to expansion, because of their “party politicking”.

He said the noise from aircraft was “appalling” for his constituents, but the Government’s decision not to introduce mixed mode - which would have seen an end to runway alternation - made a “huge difference”.

He said: “The barring of mixed mode is the best thing that could have been done. BAA wanted to introduce mixed mode immediately.”

Mr Keen, who has previously described himself as a “friend” of the aviation industry, added that a third runway would “hardly affect my constituents at all.”

Susan Kramer, MP for Richmond Park and anti-expansion campaigner, said: "I feel I ought to remind (Alan Keen) that while it is important to welcome the decision to keep runway alternation, we all know that promises have been made in the past and broken over and over again.

“We would be fools not to be constantly vigilant to ensure that this promise is kept."

Barbara Reid, lead member for aviation at Hounslow Council, said the Keens were “completely ignoring their constituents and letting them down.”

She said: “They have sided with the Government rather than siding with their constituents...90 per cent of people in every survey we have done do not support the third runway.

“For Alan Keen to say that the third runway will not affect his constituents so much, I think it once again makes you realise he is not living in the same world.

“The third runway would have a devastating affect on both Brentford and Isleworth and parts of Feltham and Heston, with thousands of people coming under the new flight path.

“It would be disatrous for the London borough of Hounslow.”