The dispute over the choice of a Labour candidate in Watford escalated today when Unite sent a complaint to party headquarters over requests for postal votes.

The union, Britain’s largest, contacted Labour after eastern region party officials postponed the selection vote, which had been due to take place tonight, following a final hustings.

It is the latest development in a troubled contest in which Mike Hedges, a taxi driver and Unite activist, above, was excluded from the initial shortlist and later then added after his supporters argued the local panel had failed to take into account his raft of trade union nominations.

Today Unite wrote to Labour outlining what it described as “procedural complaints and inconsistencies” which it said had been raised by Hedges and Watford members.

The union raised concerns over nine areas, mainly involving applications for postal votes, the handling of membership data and approaches to members by another activist aiming to be selected.

Supporters of Chris Ostrowski, who was the candidate in June and is aiming to stand again, acknowledged errors by local officials but said complaints over the process had not been fully substantiated and claimed he had received “overwhelming” support locally.

Unite today called on Labour to ensure the selection vote is dealt with “fairly”.

“Unite is supporting candidates in many of the 76 selections that are taking place across the country. We have not once had case for complaint,” a spokesperson for the union said.

“The situation in Watford is highly irregular: a candidate’s supporter should not be walking around with blank ballot papers. The rules also state that a secure office is used for the ballot papers. In Watford, one of the candidates and the candidate’s agent had access to said office.

“This could not be ignored. All along all we have said is that the party’s democracy should respected, and that Watford Labour members should be allowed every opportunity to chose their candidate fairly.”

The selection vote is now expected to take place next year. It is understood that applications for postal votes will now be re-run, following errors, while Watford members will retain the final say over their candidate.

A spokeswoman for Labour said: “The Labour Party is proud that local party members can participate in the democratic selection of their own local candidates. We are satisfied that selections are taking place in line with Labour’s rules and procedures.”