By Ben Davies BBC News Online political staff

Union leaders never tire of firing warning shots across the bows of New Labour.

But at this year's TUC conference in Brighton there is a higher than average chance they will find their target, according to Dave Prentis, general secretary of Unison, Britain's biggest trade union.

I can't see us lying low in the run up to the election if the government does adopt right-wing policies Dave Prentis

The unions recently returned from a top level policy forum, armed with a 56-point policy commitment from Labour.

But before the ink had dried TUC General Secretary Brendan Barber was warning about a potential "stitch up".

Mr Prentis is similarly wary of being taken for granted by the politicians.

But despite this, and union bitterness over Iraq and the firefighters dispute, and now, the threat to civil service jobs, he is in a cheerful mood when we meet at Unison's central London HQ.

He says he is looking forward to an "upbeat" week in Brighton,

Asked if he thinks Tony Blair should quit, he replies slightly mischievously that he is "not looking for regime change in London".

On the edge?

But, he adds, in reference to Mr Blair's reported leadership "wobble" over Iraq, "I think he nearly did in June. I think he may have come through it."

"I think he could well have been on the edge and I think people from the Treasury probably thought he was on the edge as well," he adds, in a veiled reference to Gordon Brown's supposed leadership ambitions.

But with Mr Blair still in Downing Street the boss of Britain's biggest union feels that relations with New Labour are at an important turning point.

That he attributes in no small part to the new strategy of the four big unions Unison, GMB, TGWU and Amicus of working together - thereby avoiding being "picked off one-by-one" by ministers.

Prentis believes strides forward have been made in four key areas: pensions, manufacturing, fairness at work and public services.

United?

But he knows he and his colleagues may still have a fight on their hands and it is one that the union movement and Labour's future relationship with it depends on.

"We have established 56 commitments which were given to us as a result of the Warwick Labour Party policy forum and that was as a result of intensive negotiations with secretaries of state, government ministers and political advisers in the run up to the July meeting.

"What we are about now is to make sure that at the TUC the unions remain united that we have a very strong line, a very strong message, and that message is that the commitments that have been given to us have now got to be turned into real agreements.

"If there is a message to go with all that it's that if the hierarchy of the Labour Party, if the government, reneges on the commitments it has given, there will be a price that has to be paid."

But Prentis himself admits that in the past understandings have been reached "and then forgotten about" and if that happened again it would "cause us all problems".

Last chance?

Asked if that's because it would look like the union have been "had" he replies: "Yes and we know that's not the case."

The reality is, of course, that he does not know that is the case - he can only hope a third term Labour government would come through for its traditional allies.

Mr Blair has not always had an easy relationship with the unions

He admits that the pledges that came out of the National Policy Forum in Warwick are "probably the reason we are going to say to our members we need to keep a Labour government".

But he warns: "I can't see us lying low in the run up to the election if the government does adopt right-wing policies."

Prentis's dilemma has always been just how far he should engage with Labour - remembering that there are plenty in the trade union movement who have long since given up on Tony Blair.

Conviction

He says he feels frustrated with the leadership, arguing that some of New Labour's inner circle of advisers counsel their ministers unwisely.

And that they won't listen to advice that challenges their orthodoxy on the use of private capital in the public sector.

"Tony believes in conviction politics and its quite difficult to present him with facts that he doesn't agree with," Prentis says.

"It's my job to take our views into government departments including Downing Street. I only go there if I think there's something I do want to say to them. It's not a social call. I don't do private dinners."

Unlike Digby Jones apparently.

'After-dinner speaker'

The CBI boss recently attacked unions saying they were in danger of becoming irrelevant.

"I thought it was laughable, it was meaningless, it was Digby being Digby," says Prentis.

"He's an after dinner speaker. But comedians are after dinner speakers as well."

So did Mr Jones get a fee for addressing last year's TUC?

"I don't think so. And if unions are irrelevant why did he come and why did he devote half his speech to them?"