A string of defecting British National Party members now standing for the National Front and the English Democrats Party in May's local elections has sparked fears that the extreme right could gain political power through the back door.

Defections, suspensions and expulsions from the BNP have shown signs that the beleaguered Nick Griffin leadership continues to be challenged while the BNP faces mounting financial debts. The party is defending 11 council seats and fielding far fewer candidates in this election, after losing all but two of the 28 seats it defended last year.

But the deadline this week for nominations for council elections on May 5 has seen high-profile BNP activists announce last-minute defections to other parties.

One this week was former BNP Leeds councillor Chris Beverley, currently the right-hand man of the BNP's European minister Andrew Brons. Mr Beverley, a former Morley South councillor who was ousted in last year's election, has said the figure of six million Jews murdered in the Holocaust was "not beyond debate."

He has now defected to the English Democrats Party, a move which he described on his blog as a "huge decision". He plans to stand again for Morley South. But at the same time in a conversation on Facebook he hinted at maintaining strong allegiances to Eddie Butler, who has headed challenges for the BNP's leadership after his expulsion from the party.

It has also emerged that the National Front is fielding 30 candidates throughout England and Scotland, of whom six are ex-BNP members.

A spokesman for the anti-fascist magazine Searchlight said May's election posed a "golden opportunity" for voters to dismantle the BNP as a political force.