There is a Thatcher bounce to be had, but David Cameron is not having it, according to a new Guardian/ICM poll.

Britain's longest-running polling series shows the Conservatives have clawed back just one point from last month to stand at 32%. That leaves them six points adrift of Labour, which slips back one to 38%. The Liberal Democrats stand still at 15%, while Ukip bounces up two to 9%.

The combined total of the assorted other minor parties edges down one to 7%.

The finding that the continuous coverage of Margaret Thatcher since her death has had little effect on voting intention is in line with the finding of other polls published in recent days.

ICM State of the parties Photograph: Graphic

ICM also asked voters what they would do if the Conservatives' greatest election-winner were back in charge – and found she would deliver a dramatic advantage for the Tories.

After voters were asked to "imagine for a moment that a younger Margaret Thatcher were the leader … instead of David Cameron", the Conservative vote share shot up by eight points to a potentially majority-winning 40%, putting them three points ahead of Labour, who would slide back one to 37%.

The big Thatcher boost for the Tories would come instead from Ukip, who would surrender almost half their share to stand at 5%, and from the Lib Dems, who would sink four points to 11%.

ICM applied its full methodology to this hypothetical question, adjusting for likelihood to turn out, as well as making imputations for respondents who would not reveal how they will vote.

Asked to select the politician who can best be described as Thatcher's heir, 16% choose Cameron, only one point more than the 15% who nominate Tony Blair. Boris Johnson is named by 12%, the home secretary, Theresa May, by 5%, and Ukip's Nigel Farage by 3% – the same proportion who nominate Gordon Brown.

Even among Conservative voters, the prime minister's claim to the Iron Lady's mantle is not assured – just 22% of Tory voters name him as Thatcher's heir, while 17% nominate Johnson, 12% Blair, 5% May and 2% Farage.

ICM Thatcher effect Photograph: Graphic

Cameron's failure to cash in on the Thatcher dividend is also evident in his personal ratings: across the electorate, 39% rate him as doing a good job against 49% who say he is performing badly. The difference between those two figures gives him a net score of -10, statistically indistinguishable from the -11 score he notched up when these questions were last asked almost a year ago, in May 2012.

The personal score for his Lib Dem deputy, Nick Clegg, is -29, again virtually unchanged from -27 last spring.

In line with the personal ratings of Cameron and Clegg, the coalition government as a whole remains saddled with the unpopularity it has endured for a year: 51% say it is doing a bad job, and only 31% rate it as performing well. That gives a net score of -20, in line with the -21 notched in May 2012.

The only sign of a political fightback on the part of the government comes in the ratings of the chancellor, George Osborne. A year ago, in the immediate aftermath of the budget, he was under-performing the government with a net approval rating of -25. He has now recovered to a negative but more respectable -14, with 46% saying he is doing a bad job, against 32% who regard him as doing well.

If Thatcher's death has, for the most part, had little impact on the standing of today's Tories, it may have damaged Ed Miliband. Although Labour's one-point slippage from last month is not in itself significant, his lead in the Guardian/ICM series has now halved from 12 to six points in the two months since February. Worse, his personal ratings are sinking deeper into negative territory – a majority of 51% say he is doing a bad job, as against just 28% who think he is doing well.

That gives a net approval rating of -23, almost double his negative May 2012 score of -12, and worse even than the -17 he notched up in December 2011, when his party was behind in the polls overall and his leadership appeared insecure.

The one serving party leader who appears to have gained most from the week-long focus on Thatcher is Ukip frontman Farage, who has written in Monday's Times that the need for his anti-European outfit would never have arisen if the Iron Lady had remained in office for long enough to veto the Maastricht treaty.

After his tour of the country to promote Ukip candidates in local elections next month, Farage not only has the satisfaction of seeing his party climb two points since March, but also emerges as Britain's most popular – or, more accurately, least unpopular – political leader. The 28% who say he is doing well compares with 29% who regard him as doing a "bad job", a virtual dead heat which gives him a net approval score of -1.

The breakdown of support for the other minor parties is as follows: Scottish nationalists 3%, Greens 2%, Plaid Cymru 1%, British National party 1%, other smaller parties 1%.

• ICM Research interviewed a random sample of 1,005 adults aged 18+ by telephone on 12-14 April 2013. Interviews were conducted across the country and the results have been weighted to the profile of all adults. ICM is a member of the British Polling Council and abides by its rules