According to reports from the BBC, incumbent Derek Simpson, Unite joint general secretary, has hit out at his rival Kevin Coyne accusing his bid as being "all about personal ambition".

The BBC reported that Coyne has labelled the comments, which were allegedly leaked from a private letter, "absurd".

The election challenge came following a challenge to the certification officer after a vote from Unite members on a new rulebook which provided for Simpson to remain in his position for an extra year, beyond the mandatory retirement age of 65.

An election is to be held next February preceding the 2010 election to appoint a single leader of the merged unions of Amicus and the Transport and General Workers' Union (TGWU).

The leaked letter will fuel rumours of infighting at the union, following reports last month of a breakdown in the relationship between Simpson and TGWU boss Tony Woodley, which led to Unite releasing a statement insisting the two shared a "warm friendship".