The Advertising Standards Authority last week rejected a complaint about a Greenpeace advert that said 100 Labour MPs were "untrustworthy" on the subject of climate change.
The advert, which was run as a one-off in The Guardian, named 100 Labour MPs who voted in November to reject amendments to the Housing Bill that would have required the Government to improve home energy efficiency by 20 per cent by 2010.
The Greenpeace advert claimed that the MPs had previously supported an Early Day Motion calling for improved home energy efficiency but "caved in to pressure from Tony Blair".
This prompted one of the MPs to complain to the watchdog, arguing that the ad was misleading because it implied they originally supported the amendments when in fact they had only signed up to an EDM.
"They argued that they didn't commit to anything by signing up to the EDM, which we disagree on," said a Greenpeace spokesman.
The international environmental organisation said that constituents were misled because they would have expected MPs who supported the EDM to vote in favour of the amendments. "The Government did not live up to its rhetoric on climate change," said the spokesman. "We can't let politicians get away with this sort of thing."
The ASA rejected the unnamed MP's assertions that the ad was misleading and that it portrayed the MPs unfairly.
But the watchdog upheld the complaint on two points. It ruled, first, that Greenpeace could not prove the MPs had bowed to the Prime Minister's will; and, second, that it could not substantiate its claim that 30,000 people die each winter because they cannot afford to heat their poorly insulated homes.