The Conservatives’ post-party conference bounce is well and truly over, according to the latest Opinium/Observer poll which gives Labour a seven point lead over the Tories.

David Cameron’s party went ahead of Labour in some polls immediately after the prime minister promised tax cuts for middle earners in his conference speech in Birmingham earlier this month.

But Opinium now has Labour up one point on a fortnight ago on 35%, the Tories down four on 28%, Ukip unchanged on 17% and the Liberal Democrats up two on 9%, a possible boost resulting from the Lib Dem conference which ended last Wednesday. The Greens are on 4%.

Photograph: Opinium/Observer

Ed Miliband’s personal rating will be a source of alarm for Labour, however. He now stands on -26%, compared to -6% for David Cameron. This is the number of people who approve of his performance, minus the number who disapprove.

Despite giving Labour a 7pt lead more people now expect the Conservatives to win the next election than Labour. This is a reversal of the finding when the question was asked last year.

Photograph: Opinium/Observer

Only 13% think the Conservatives will have a majority after the election, while 27% think they will be the largest party in a hung parliament, meaning 40% think they will come out on top.

Last September 11% thought the Tories would win a majority and 25% that they would be the largest party (a total of 36%).

Just 14% now think Labour will win a majority and 24% that they will be the largest party in a hung parliament, meaning 38% believe they will emerge as winners. Last year 27% said Ed Miliband’s party would emerge as the largest in a hung parliament and 16% that they would win a majority giving a total of 42%.