GMB general secretary John Edmonds - a prominent and outspoken critic of Tony Blair's public service reform agenda - will resign today.

It is expected that the union boss will make an official announcement to the GMB executive later this morning.

Edmonds, who had been set to quit at the end of next year, is expected to play a stronger role in the pro-euro campaign.

The move will lead to a fierce leadership contest between London region leader Paul Kenny and Northern region leader Kevin Curran - both of whom describe themselves as centre-left.

But Downing Street cannot expect an easy ride in Edmonds' absence - both Kenny and Curran are pledged to continue the GMB's campaign against the prime minister's public service reforms.