The far-right British National Party could gain a seat on the London Assembly, according to the latest opinion poll.

A survey for the Evening Standard by polling firm YouGov also found the gap between Ken Livingstone and Steve Norris had narrowed, along with support for the BNP at the crucial five per cent threshold.

This could see the far-right party, which calls for all immigration to be stopped to ensure "the British people retain their homeland and identity", take a seat on the Assembly.

Voting for the mayoralty, the London Assembly, and the European Parliament will take place on the same day, June 10.

Meanwhile, the race for the Mayoralty looks to be between Mr Livingstone and Mr Norris, after the YouGov poll of 1,350 people showed support for Liberal Democrat Simon Hughes at about 17 per cent.

Mr Livingstone, who won the 2000 election as an independent but recently rejoined Labour, polled 40 per cent, while his Tory rival Steve Norris, was on 31 per cent.

Under the rules of the preferential voting system, if no candidate wins more than 50 per cent of votes, the top two polling candidates will go into a run-off.

At this stage, the amounts of second preferential votes are added to the first votes to decide the winner.

While support for Mr Livingstone has dropped since he moved back into the Labour camp, Mr Norris has gained about 5 per cent since late last year.

The level of support for Mr Hughes will be a clear concern for the Liberal Democrats, exactly one month ahead of Election Day.