Conservatives and Labour both take hit as anti-European party gets boost from leader's decision to stand in 2015 election

Ukip have taken a shock six-percentage-point leap in the polls following confirmation that Nigel Farage is intending to stand in a Tory seat in Kent. An Opinium/Observer poll has Farage's party on 21%. It appears that Ukip has taken support from both the Tories and Labour.

Ed Miliband's party is down three points, leaving it on 32%, and the Conservatives are down four points to 28%. The Liberal Democrats have enjoyed a small rise of three points to 10%.

Last week Farage confirmed that he will put his name forward to stand as Ukip's candidate in Thanet South. Farage stood in the constituency in the general election of 2005, when he came fourth, but his party has seen a huge surge in popularity in the intervening period.

Kent was among the southern and eastern English counties where Ukip performed particularly strongly in the recent European elections in which the party topped the polls. The anti-EU party has also won a string of local council seats in Kent.

• Opinium Research carried out an online survey of 1,963 GB adults aged 18+ from 12th to 15th August 2014. Results have been weighted to nationally representative criteria. Full tables and results are available here.