Labour's lead over the Tories has been cut to seven percentage points, with Ukip enjoying a new surge, according to the latest fortnightly Observer/Opinium poll.

After two weeks in which immigration and energy prices have been in the news, the high level of support for Nigel Farage's party will be a worry for all three mainstream parties.

Labour is down two points at 35% while the Tories are unchanged on 28%. Ukip is the only party to gain, up three points to 19%, while Nick Clegg's Liberal Democrats are down one point on 8%.

The net personal ratings for leaders are little changed, showing David Cameron on -18, with 33% approving of his performance and 51% disapproving.

Ed Miliband, meanwhile, is on -23, with 24% approving of his leadership and 47% disapproving.

Clegg is on -46, with 14% approving and 60% disapproving.

• Opinium Research carried out an online survey of 1,941 GB adults aged 18+ from 26 to 29 November 2013. Results have been weighted to nationally representative criteria. Full tables and results (pdf)