On the eve of the Labour conference, the Conservatives sought to unsettle Ed Miliband by releasing private polling showing that most voters believed David Miliband would have made a better leader and that Miliband lacked the qualities required of a prime minister. Now, as the Tories head to Birmingham for their annual gathering, Labour has released its own mischevious poll.

After Miliband alleged in his conference speech that David Cameron would receive the "millionaire’s tax cut", a private poll for the party by ICM (sample size: 2,009) has shown that a majority of voters want Cameron to say whether he will benefit from the abolition of the 50p rate. Asked whether the Prime Minister should "come clean and tell people honestly whether he is personally benefitting from this" or whether it was "a matter only for him", 62% said the former and 22% the latter. Among Conservative voters, 46% wanted Cameron to "come clean", while 40% agreed it was a private matter.

Aware of how much damage the Tories inflicted on Ken Livingstone over his tax arrangements (and with an eye to how the Obama campaign forced Mitt Romney onto the defensive over his tax bill), Labour is out for revenge. Miliband used the final PMQs before the conference season to challenge Cameron on whether he would benefit from the 50p tax cut, describing it as "a question he would have to answer between now and April" (when the tax cut is formally introduced). Cameron has so far refused to give an answer (unlike George Osborne, who said he would not benefit from the move) and, under ever-greater pressure from Labour, the Tories will need to decide whether this strategy is sustainable.

The poll also reminds us just how unpopular the decision to abolish the top rate is. The survey, conducted on Wednesday and Thursday this week, found that 71% of voters think the coalition should abandon the tax cut. Asked whether, "with government borrowing coming in higher than expected", the government should "cancel plans to cut tax for people on £150,000 a year", 45% strongly agreed it should, while 25% somewhat agreed. Seven per cent strongly disagreed that it should and 10% somewhat disagreed. By 65% to 26%, Conservative voters also opposed the tax cut going ahead. 

Were this not a private poll, it's unlikely that the question would have appeared in that form ("with government borrowing coming in higher than expected" is designed to lead voters to the desired answer) but it's worth remembering that previous polls have shown widespread opposition to the abolition of the 50p rate. An ICM survey for the Guardian in March found that 67% of voters wanted to keep the top rate. More than any other single measure, it was the abolition of the 50p rate, juxtaposed with tax rises on pensioners, pasties, caravans, churches and charities, that retoxified the Tory brand.