Allegations of foul play in a Birmingham City Council byelection are flying fast, with Liberal Democrat and Labour parties accusing each other of misconduct.

The poll, in Aston on July 28, was called when three Labour councillors were expelled from office after an election court heard how they helped organise a campaign of postal vote fraud.

One of them, Muhammed Afzal, was cleared by the Court of Appeal but his case is now the subject of a House of Lords deliberation.

The other two - Mohammed Islam and Mohammed Kazi - were banned from voting in the by-election or playing any part in canvassing and campaigning.

Labour ward organiser Zulfiqar Khan was also subject to a banning order after the court found him guilty of "corrupt and illegal practices".

Liberal Democrat spokesman Ayoub Khan, a candidate in the by-election, has filed an official complaint alleging that Mr Islam, Mr Kazi and Zulfiqar Khan have been campaigning for Labour.

The claim, if proven, could invalidate the by-election and force a second poll to be held.

Mr Khan said: "Our agent has spoken to the Labour agent. We have seen Zulfiqar Khan going in and out of the campaign office on numerous occasions."

Ayoub Khan said he would instruct solicitors to pursue a contempt of court action against Zulfiqar Khan.

A West Midlands Labour spokeswoman confirmed that Zulfiqar Khan entered the Aston Labour campaign headquarters on Monday, against the party's wishes.

She said Mr Khan had been written to twice by Labour ordering him to "stay away from out campaign".

She said she could find no evidence that Mr Kazi or Mr Islam had been taking part in the campaign.

Labour, in a separate development, has reported Lib Dem candidate Abdul Khalique to the Director of Public Prosecutions for allegedly failing to submit an election expenses form when he contested Lozells and East Handsworth ward as an Independent candidate in 2004.

The Representation of the People Act, which governs the conduct of elections, describes the failure to this form as an "illegal practice".

Labour's West Midlands spokeswoman said: "We have contacted the city council elections office and the Electoral Commission. They both said they could not find a return from Mr Khalique.

"We regard this as a very serious offence, particularly since the Liberal Democrat election slogan is 'the team you can trust'."