Labour is unchanged on 33%, the Tories are up three points on 32%, Ukip is down one point on 19%, and Lib Dems have dropped by two points to stand on just 7%.
The poll confirms the recent overall trend, which has seen Labour's lead over the Tories cut markedly since early in the year. The one-point lead is the equal lowest Opinium has recorded in its series with the Observer, which began in 2012.
While the Tories will be pleased by the narrowing of the gap with Labour, the party's inability to push its own tally up higher to a point where it could entertain the prospect of an overall Commons majority will be a worry, particularly after a rush of good economic news.
Labour's score will fuel discontent over its performance, and that of its leader, Ed Miliband, after less than impressive local election results.
The poll also asked voters their opinions on rising house prices. While 35% said that the trend was good for them and their families, 44% said it was bad for the country generally. Half thought the government should intervene to prevent a housing bubble.
Tory voters are narrowly against government intervention, while Labour voters heavily support intervention in the housing
Around a third (34%) of voters say the Bank of England should raise interest rates to prevent a bubble, while 36% think they should remain the same.
• Opinium Research carried out an online survey of 1,968 GB adults aged 18+ from 20 to 23 May 2014. Results have been weighted to nationally representative criteria.
guardian.co.uk © Guardian News and Media Limited 2010