A fresh vote-rigging investigation is under way in a Birmingham ward where the British National Party won a disputed city council election last month.

The BNP said last night that at least five supporters of the far-right party voted in Kingstanding on May 4, but on the council's official polling register they were shown not to have voted at all.

A sixth BNP supporter, who insists he did not vote, appears on the register as having voted.

Police have been asked to investigate and the city council said last night it would assist the inquiry.

Sharon Ebanks was declared the winner in Kingstanding, but then told by the council that BNP votes had been double counted and that Labour's Cath Grundy ought to have been elected instead.

Labour has submitted an election petition to the High Court in an attempt to have Coun Ebanks replaced by Ms Grundy. A preliminary hearing will take place tomorrow.

Birmingham City Council blamed the mix-up on a mistake in the counting process, which saw more than 2,000 votes counted twice. Although Coun Ebanks was declared the winner with 2,310 votes after two re-counts, the true figure should have been 1,329 according to the council.

BNP Midland organiser Simon Darby has been examining the marked registers kept by clerks at all of the Kingstanding polling stations.

The registers show who on the electoral roll voted and who did not.

Mr Darby said: "We have spoken to people who we know would have voted for us and they have confirmed that they did indeed do so. Yet on the register they are shown as having not voted.

"We are not happy. There is definitely something not right about this election."

Coun Ebanks said: "We have people who would be prepared to stand up in court and say they voted for us."

A spokeswoman for Birmingham City Council said: "We understand that allegations of possible fraud have been made to police. We will assist the police in their inquiries as required."