By Ben Davies
BBC News political reporter
Labour would have difficulty winning the next election with Gordon Brown at the helm unless its policies change, the boss of a leading union says.
Mr Simpson says Labour cannot win without its core vote
Amicus leader Derek Simpson - seen as a Brown supporter - said the chancellor lacked Tony Blair's charismatic ability to sell Mr Blair's "crap" policies.
He said a complete change of direction was needed to save Labour from defeat.
Amicus is the largest private sector union and gave £2m to Labour at last year's general election.
It also loaned Labour cars, phone lines and campaigning support and recently struck an agreement to give the party a quarterly donation, handing over the first instalment of £500,000 to party chairman Hazel Blears on Tuesday.
With Labour under pressure to repay donations from wealthy individuals the union's financial support will be more welcome than ever at Labour HQ - as will the union's ability to mobilise its members in the party's cause at election time.
But Mr Simpson made clear such support comes with a price.
In an interview with the BBC News Website, he said it would be hard to motivate the union's "troops" to help Labour win a fourth term unless the party changed direction.
He said: "Blair's lack of policies are in trouble - and it will get worse under Gordon Brown because he will not be able to sell the crap policies."
"Labour would have difficulty winning next time even if Steven Gerrard (Liverpool football club's cup winning captain) were playing for them."
It is a change of tone from Mr Simpson who told the Times in 2004 Mr Brown - the man widely expected to be the next Labour leader - would be "excellently" placed to replace Mr Blair "and correctly so".
But in common with many on the left he has grown increasingly critical of Mr Brown's apparent desire to continue with Blairite reforms of the public services and what he sees as its failure to support manufacturing industry.
He is also frustrated by the seemingly interminable debate over the Labour succession - saying the party should have settled the question of who should have taken over from Mr Blair "yesterday".
And he has growing doubts about the leadership's commitment to delivering the Warwick agreement - the historic deal struck between Mr Blair and the unions before last year's election.
The idea was that the unions would receive long-sought after commitments on pensions, skills, equality issues, employment rights and public services in return for bankrolling Labour's campaign and lending campaigning support on the doorstep.
So where are they with Warwick now? "Well that's a very good question which we might ask," said Mr Simpson.
"Some aspects of Warwick have been delivered ... [but] the more contentious - and more important - issues have only partly been dealt with or not dealt with at all.
"In fact it seems almost as if there is an attempt to renege on Warwick. Certainly to draw back from some of the issues that were discussed."
The union boss's comments come after weeks of speculation about the timing of Tony Blair's exit from Downing Street.
All of the leaders of the big four unions - Unison, T&G, Amicus or GMB - have been largely quiet on the issue of replacing the Labour Party leader and Mr Simpson's decision to speak out now will be seen as a bid to increase the pressure for what he sees as long-overdue policy changes.
The ex-communist Amicus chief, who once said he would not only give Tony Blair a headache, he would give him an "effing migraine", was full of praise for the Labour leader's political skills, if not his policies.
"I think people underestimate Tony Blair. He is one of the best orators and communicators that I have ever seen. If Tony Blair came out with appropriate policies I would not be anxious to see him go," said Mr Simpson.
"Gordon I don't think has the same charisma as Blair and I am afraid he would have to have the better policies to stand a chance [of winning a fourth term]. But this I do know - what is happening now is damaging."
He and other union bosses hoped that Labour would deliver on Warwick and "that would be in turn something worth campaigning for and enough to persuade us to vote Labour again".
"[In 2005] We went into many constituencies especially into marginals and had a positive effect in seats that we believe would otherwise be lost. If we had not been able to do so Labour may not have won the last election - it could have been a hung Parliament or even a Conservative win."
Last chance saloon?
To ensure the unions' continued support, Mr Simpson argues Warwick must be delivered and by the time of the next general election campaign a "Warwick II" deal should be signed up to.
High up the union wish list is a level playing field for British workers who currently are "cheaper and easier to sack" than their EU counterparts.
Mr Simpson says on pensions that progress has been made with restoration of the link with earnings but he still wants to see compulsory contributions - the other Turner Report recommendation.
And he argues the Thatcher-era anti-trade union laws have still to be tackled. He says he is not even talking about issues about secondary picketing which has long been a sore-point for people in the union movement.
"I think it's the last chance saloon for people who want a Labour government because it is seriously difficult to see the trade union movement having a relationship with anybody other than the Labour Party," he adds.
"The issue at the moment is not just about Labour losing power, it is the consequences of what will befall ordinary working people with the difficulties a Conservative government I'm sure will place in front of them."