Sir Ken Jackson had conceded defeat in his bid to remain joint head of the Amicus trade union.

He decided not to contest the outcome, despite initially indicating he could lodge a complaint against an "unfair" campaign.

On Thursday it was revealed that he had suffered a shock defeat at the hands of left-winger Derek Simpson.

After four counts, Simpson was declared the winner by just 406 votes.

But following Sir Ken's initial refusal to accept the result, a stormy executive committee meeting saw six members walk out, leaving the union's leadership in limbo.

If the outcome had been contested, a final decision could have taken several weeks.

In contrast with Simpson, Sir Ken was seen as one of the leading Blairites in the union movement, helping to smooth over disputes with the government.

Sir Ken's decision will come as a further blow to Labour as it struggles to maintain strained relations with its union allies in the wake of a series of strikes, funding cuts and policy disputes.