The Prime Minister's favourite trade unionist, who wants to remain in charge of his million-strong union beyond his retirement age, may be forced to stand for election.
Left-wingers in the "super-union" Amicus have been advised by lawyers that Sir Ken Jackson, 64, must face a poll if he wants to stay on as joint general secretary for the next two years.
Tony Blair relies on Sir Ken's support to deliver critical votes within the Labour Party and will be concerned at any attempt to unseat him.
The only other senior figure in the Labour movement to fight to retain influence over his organisation beyond retirement age is Arthur Scargill, 64, who recently won top-level support in the National Union of Mineworkers for a new and powerful post of honorary president, in effect making him "president for life".
Whereas Mr Scargill, who led the miners' strike in 1984-85, is on the hard left, Sir Ken is on the other extreme of the movement and a powerful ally of the Prime Minister.
Sir Ken won two-to-one backing last summer from the annual conference of his own organisation, the Amalgamated Engineering and Electrical Union, to stay on until December 2004 – a decision ratified by the AEEU's national executive.
It is known that Sir Ken's plan to stay on after his 65th birthday has raised deep concerns in the white-collar union, MSF, which has merged with the engineering union to form Amicus.
Roger Lyons, leader of MSF and now joint general secretary of Amicus, had believed that he would run the new merged organisation after Sir Ken reaches retirement age this March, until his own term of office expires in 2005.
Sources at the old MSF division of Amicus yesterday said that Mr Lyons, who is to the left of Sir Ken, might rethink his own retirement date if his rival stays on.
Sir Ken has been a key figure in ensuring that Mr Blair and his allies keep a grip on the Labour Party.
The old AEEU invariably toed the New Labour line at party conferences where the trade unions still command half the vote.
Legal advice provided to Amicus left-wingers by John Hendy, a QC specialising in employment law, stated that Sir Ken would have to face an election if he wanted to remain after next January.
Mr Hendy indicated that legislation allowed union leaders to stay on for a year after retirement date in the wake of an amalgamation. Amicus was formed on 1 January 2002.
Mr Hendy argued that Sir Ken would have to submit himself for re-election if he wanted to remain thereafter.
Derek Simpson, a left-wing Amicus official based in Derby who sought the legal advice, alleges that the union's executive was misled into believing that Sir Ken could lawfully stay on until 2004 without facing an election.
Last night, officials close to Sir Ken said they believed he would submit himself to a poll if necessary. However they understood that he was in his rights to remain in post without an election.
The two organisations were at daggers drawn in the run-up to the merger, partly because of a row over Mr Lyons' expenses and partly because of deep political differences.
Amicus is Britain's biggest manufacturing union and second in size only to Unison, the 1.3 million-strong public service union.
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