Pro-expansion lobbyists have had an advert banned and been warned not to repeat misleading claims that 'most people living in communities near Heathrow Airport support its expansion'.
The Advertising Standards Authority published its ruling, on Wednesday April 8, against Back Heathrow and added the group must also stop saying "independent polling shows 60 per cent of local residents, expressing an opinion support expansion."
The advertisement must not appear again in its current form.
Anti-expansionists HACAN, said the decision was "a real blow" to Back Heathrow's strategy of convincing decision-makers a majority of local people backed a third runway.
While Back Heathrow said the ruling was confusing because "even by the ASA's own definition of residents living near to Heathrow, the evidence clearly shows a majority of support for the airport's expansion".
The advert in question appeared on October 12 and 16, 2015, and was headlined "Rallying for the runway".
Further text stated "Don't believe the hype. Most people living in communities near Heathrow Airport support its expansion".
The ad claimed to be based on responses from 12,004 residents of Spelthorne, Richmond Park, Brentford & Isleworth, Feltham & Heston, Windsor, Ealing North, Ealing Southall, Uxbridge & South Ruislip, Slough, Hayes & Harlington, Beaconsfield and prompted complaints from five people.
An ASA spokesman said: “Given that a significant number of respondents, who had expressed an opinion albeit a neutral one, had been excluded from the sample, we considered that this was not a suitable methodology by which to draw such a conclusion.
"We considered the evidence held by Back Heathrow demonstrated only that 50 per cent of all those polled were in support of expansion.
"Therefore, we concluded it did not substantiate their claim that “most people living in communities near Heathrow Airport support its expansion” which was likely to be understood in the context of the statement “… 60 per cent of local residents expressing an opinion support expansion”".
Consequently, it said, the ad breached its code.
John Stewart, chairman of HACAN, the campaign group which opposes Heathrow expansion, said: “This ruling is a real blow to Back Heathrow as a cornerstone of its strategy has been to try to convince decision-makers that a majority of local people back a third runway.
"These claims are now starting to unravel.”
Back Heathrow reiterated its view that according to the ASA's own definition of residents living near to Heathrow, "evidence clearly shows a majority of support for the airport's expansion".
A spokesman for Back Heathrow said: "Nevertheless, we are pleased that the ASA acknowledged that more local people support a new runway at Heathrow than oppose it.
"In the recent Airports Commission public consultation, 82 per cent of the 70,591 responses were in favour of Heathrow expansion. Most of these were local residents so we think the ASA is on wafer-thin ice with this ruling.
"In the 10 constituencies defined as 'local' by the ASA, there is a 53 per cent majority in favour of Heathrow expansion."