Tariq Mahmood (40) of Clarence Road, Maqbool Hussein (52) of Ledbury Road, Netherton, and former Mayor of Peterborough Mohammed Choudhary, (49), of Cobden Street, all rigged votes in a botched attempt to win seats in the 2004 local elections.

Choudhary and Hussein were Central ward candidates at the elections.

Yesterday, after more than 66 hours of deliberation, a jury at King's Lynn Crown Court returned guilty verdicts for all 14 forgery charges against Mahmood.

Choudhary and Hussein had each been found guilty of four charges of forgery earlier in the week.

After the verdicts were read out by the jury foreman, Deputy Circuit Judge Alan Hitching told the men: "You all face immediate custodial sentences. The only issue will be how long those sentences are."

The three men "hijacked" postal and proxy vote application forms from voters in the Asian and Portuguese communities in the run-up to the Central ward elections, and filled some of them in themselves.

The votes were sent to a number of hub addresses, where the ballot papers would be filled in.

However, despite their efforts, the Labour candidates were all beaten by Conservative election candidates.

The jury spent more than two weeks discussing the verdicts – thought to be among the longest deliberations in British history – before reaching the decisions at 3.45pm.

Judge Hitching praised the work of the eight women and four men and said: "We have all admired the conscientious way you have gone about your task, going through defendant by defendant, count by count."

Today, Detective Inspector Ian Tandy, who led the investigation, said: "This has been a long and complex investigation into a systematic and organised campaign of electoral fraud. The investigation is ongoing.

"Electoral fraud will not be tolerated. It is a democratic right for each person to vote for who they want with privacy and the stealing of an individual's vote is not acceptable."

Jurors were still deliberating on four further counts of forgery against Choudhary, and three against Hussein.

Choudhary was also found not guilty on two counts, while the jury returned one not guilty verdict against Hussein yesterday.

All three were bailed for reports and will be sentenced on April 7.