A police hunt is under way to find five witnesses who claim they are too frightened to give evidence at a trial into alleged Labour Party election smear tactics in Birmingham.

Officers were called in by a judge who warned the five could face contempt of court proceedings if they continued to refuse to attend an election court hearing into allegations that Muhammed Afzal won a council seat in Aston in May this year after spreading lies about his Liberal Democrat opponent.

Recorder Timothy Straker QC, sitting as Elections Commissioner, said it was "imperative" that the Director of Public Prosecutions took an active interest in the case.

Mr Straker, sitting as Elections Commissioner, is trying an election petition brought by Saeed Aehmed, the losing Lib Dem candidate in Aston at the 2007 elections, which claims that Coun Afzal and his family ran a smear campaign with the backing of the West Midlands Labour Party.

Coun Afzal (Lab Aston), who won the seat with a majority of more than 600 votes, is said to have published false statements and issued claims that Mr Aehmed was arrested for postal vote fraud and was also guilty of making fraudulent applications to the council for disability grants.

The smears were false statements contrary to the Representation of the People Act and made it impossible for Mr Aehmed to gain enough support from voters to win the seat, according to the petitioners.

A dramatic day in the trial at Birmingham County Court was told that three witnesses had submitted written statements but were too frightened to attend in person to be cross-examined.

They were Mrs Asmat Mir, Iqbal Khan and Abdul Aziz.

Two others, Muhammed Amid and Muhammed Banaris, the cousins of Liberal Democrat city councillor Ayoub Khan, are required by the petitioners to give evidence but have complained of being "warned off" attending, it was said

The addresses of the five were not revealed in court, but one, Abdul Aziz, is understood to have left Birmingham.

A second, Iqbal Khan, sent a sick note to the court, signed by a doctor, stating that he was suffering from "dizziness and general debility" and should refrain from work for 13 weeks.

Gerry Bermingham QC, for the Director of Public Prosecutions, said police would try to find the reluctant witnesses and tell them to come to court "or else".

All of the allegations levelled by the petitioners are denied by both Coun Afzal and Labour officials.

Gavin Millar QC, representing Labour, described reports of witness intimidation as unsubstantiated innuendo which the Liberal Democrats were "putting a gloss on". He said it could be the case that the people had been pressured into making statements and were now having second thoughts about coming to court.

Mr Millar added: "We want it all out. Our preference would be for all five to give evidence."

Graham Brodie, for Mr Aehmed, produced a copy of an email from Abdul Azad, who had submitted a written statement but was refusing to attend the court to be cross-examined.

The email read: "Until I get security for me and my family I will not come to court to testify. I have had a lot of threats from the Bangladeshi community in Birmingham."

Mr Brodie said: "What it comes down to is we have a number of witnesses who are saying, to put it conservatively, that the atmosphere within which these proceedings are being conducted is such that they are reluctant to attend.

"I do not propose to seek notice asking them to show cause. I do not want to commit those who have been too scared to attend.

"If there is to be further investigation as to the reasons why these people aren't present, my position would be that is an investigation which ought properly to be conducted by the police."