Equal Marriage: Equal Polls?

With almost uncanny timing Populus have released yet another poll on gay marriage.
Their survey says... support is now at 65% - or a more headline-hugging two-thirds.
This is up from 61% from the oft-cited poll that Populus conducted for The Times in 2009.
Oft-cited by gay marriage advocates, that is.
The result is significantly higher than support shown in recent polls by both the Telegraph/ICM (45%) and The Sunday Times/YouGov (43%).
And it's three times as high as the loopy poll Catholic Voices/ComRes poll which had 22% for gay marriage, but 70% against.
How Catholic Voices/ComRes skewed their "findings" with a heavily loaded question has been pulled apart, but why is there such a large disparity between Populus and The Sunday Times and Telegraph?
The statement Populus asked people to agree or disagree with seems pretty straight-forward; "Gay couples should have an equal right to get married, not just to have civil partnerships".
But the ever fascinating and pretty reliable Full Fact argues that how all of the four pollsters phrased their questions may have influenced their results.
"The ICM and YouGov polls present the most neutral statements as the stimulus for soliciting an opinion, while the ComRes and Populus polls present arguments and ask for affirmation or opposition. The former polls produce similar results while the latter polls show the most extreme findings in favour and in opposition to the Government's plans.
"So while none of the polls on gay marriage are invalid, the methods used by each of them need to be serously taken into account before conclusions are drawn in news reports."
Populus may have asked a leading question, just like Catholic Voices/ComRes did - the technical term here apparently is "affirmation bias" - and support for gay marriage could be markedly lower than the titillating two-thirds they suggest.