Charlie Whelan, Brown's awkward link with the union

Ken Clarke, the shadow Business Secretary, drew the obvious link yesterday between Gordon Brown and the union involved in the BA strike.

"There is no point in being naive," he said. "The fact is that Unite has given £11m to Labour over the past four years. They own the Labour Party, which is why there is no condemnation of any kind coming for a particularly irresponsible strike. They are totally silent because their silence has been bought."

Given the close personal ties between the union and the Labour Party, an obvious question is why Unite should call a strike that could embarrass the Prime Minister at such a politically sensitive time. Why could Harriet Harman's husband, Jack Dromey, deputy general secretary of Unite and prospective Labour MP for Birmingham Erdington, or Brown's former spin doctor, Charlie Whelan, political director of the union, not simply have arranged to delay the dispute until the general election is over?

The answer is that Unite is not a monolith. With nearly 1.6 million members, it is the biggest union there has been in Britain since the 1980s, and like any large political organisation it has a mass of factions and competing ambitions.

It does not even have a single boss, but two general secretaries, Tony Woodley and Derek Simpson, who were the respective heads of the Transport and General Workers Union (TGWU) and the manufacturing union, Amicus, until those two giants came together in an uneasy marriage in May 2007.

Mr Woodley and Mr Simpson are rivals rather than partners, with separate bands of supporters. Of the two, Mr Simpson is closer to the Labour leadership. Mr Woodley is less interested in politics, but his instincts are well to the left of Gordon Brown's.

When the two men retire, Unite will have a single boss for the first time. Len McCluskey, who is handling negotiations with BA, is a leading candidate for the job. To judge from the praise he was receiving yesterday on an internet chatroom used by members of Bassa, the publicity he is getting will boost his campaign. He is assumed to be Mr Woodley's preferred successor, which means he is not Mr Simpson's.

Bassa is an independent union that merged with the TGWU nearly 20 years ago, but is still run mostly by shop stewards rather than officials fom Unite.

When Bassa was threatening to stage a 12-day strike over Christmas, before the High Court ordered Unite to call it off, Derek Simpson sounded as if it had nothing to with him. Asked to explain the strike on GMTV, he said: "It was the decision of the negotiating team in BA. That's their judgement of what's needed to bring sense to this. It's probably over the top." Those remarks went down very badly with Bassa shop stewards.

Yesterday, a union spokeswoman said: "There is no grand plan here. It's just 15 months of an intransigent management and very strong feelings in the workforce."