Campaigners claim that Theresa May would run into trouble locally if she backed a third runway at Heathrow.

Lobby group HACAN, which is against Heathrow expansion, has unearthed a poll which shows that less than a third of residents in Windsor and Maidenhead borough, which includes the Prime Minister’s constituency, back a third runway at Heathrow.

HACAN chairman John Stewart said, “These findings show just how carefully the Prime Minister will have to tread in coming to her decision about where a new runway should be built. She risks a backlash in her own backyard if she gives the go-ahead to a third runway at Heathrow.”

The poll’s findings showed that only 31% of people in the borough backed Heathrow Airport’s plans for a third runway, with 38% opposed to it. 50% supported a second runway at Gatwick, with 14% against.

But Heathrow has hit back this week, revealing that a new poll shows 51% of people in 12 constituencies in the area supported Heathrow expansion with only 35% against.

It says more than 10,000 people were interviewed, including in Windsor and Slough.

Nigel Milton, director of external affairs at Heathrow said that after the previous proposal was rejected the airport had gone back to the drawing board and designed a new, more environmentally friendly plan.

He said: "This polling shows that a majority of our neighbours recognise that a third runway will create tens of thousands of local jobs, ending youth unemployment in the communities closest to the airport as well as reducing noise impacts and meeting air quality rules."

The Royal Borough has remained steadily opposed to Heathrow expansion - Old Windsor in particular suffers from noisy night flights.

But neighbouring Slough has largely supported the plan, apart from the village of Colnbrook which would be worst hit.

Windsor's MP Adam Afriyie opposes expansion But last month HACAN unearthed archive material from 2009 at which Mrs May spoke out against a third runway, although the plan approved by Labour back then differed substantially from the new version. It was later abandoned when the Conservatives were reelected in alliance with the Liberal Democrats.