The ad urged readers to write in protest to MPs listed in the ad, who had withdrawn their support for improved home energy efficiency targets during the passage of the Housing Bill.
An MP from West Yorkshire, whose identity the Advertising Standards Authority is unable to disclose, complained to the authority about the ad, which was headlined "No wonder people don't trust politicians".
The ASA agreed that the advertisers, Greenpeace and political pressure group Active Citizens Transform, had made two misleading claims in the ad, but cleared them on two other points.
One of the misleading claims said that the MPs listed in the ad voted against amendments to the bill, which would have increased home energy efficiency targets, because of pressure from Prime Minister Tony Blair.
Greenpeace and ACT argued that there was a whip directing MPs to vote against the amendments, which constituted extreme pressure from the government. They also produced an email received from an MP after the ad appeared that proved the MP was under pressure to vote with the government.
However, the ASA considered that the advertisers had not proved that the MPs had "caved into pressure from Tony Blair", as stated in the ad.
The second misleading claim was that was that "30,000 British people die needlessly every winter because they can't afford to heat their poorly insulated homes". The ASA judged that the advertisers could not prove that all 30,000 deaths were the direct result of inadequately heated homes.
The ASA did reject two aspects of the MP's complaint. One concerned the claim that the MPs listed in the ad originally said they would support the amendments.
The MP said that the ad confused support for the amendments with support for energy targets expressed by the signature of Early Day Motions supporting the campaign to secure an amendment supporting the targets.
The ASA said the claim was valid because it "considered that most readers would believe the MPs' public support for the Early Day Motions amounted to much the same thing as support for the amendments".
Finally, the MP's complaint that the ad unfairly portrayed the named MPs, especially by implying they were untrustworthy, was also rejected.
The ASA said it "considered that readers were likely to understand the advertisement to be an expression of the advertisers' opinion on a controversial subject". It added that because the MPs were public figures, the reference to their voting behaviour did not unfairly portray them in an adverse way.
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