Interview By Ollie Stone-Lee Political reporter, BBC News

Dave Prentis says the public are worried about NHS reforms

Dave Prentis, general secretary of public sector union Unison, said the time limit on Mr Blair's premiership meant ideas had been ill-thought out.

The way ministers were "privatising" part of the NHS was wasteful and would see big hospitals close, he says.

His warning comes as the TUC congress opens in Brighton.

Some union leaders are calling for the prime minister to go immediately but Mr Prentis says he is looking at long-term policies.

There is no chance of Labour winning a fourth term unless there is a change of direction, something not guaranteed by a change of leader, he tells the BBC News website.

None of Unison's 1.3m members can believe the course pursued by a Labour government which they helped to a historic third election victory last year, he says.

'Tidal wave'

Mr Prentis sees Tony Blair's "foolhardy" decision to announce in 2004 that he would step down before the next election as an important driver for the reforms.

"I think the prime minister, realising it was time limited and worried about all the effects of his unpopular policies on Iraq and more recently the disastrous policy on Lebanon, wanted a legacy," says Mr Prentis.

"And I think he sees that coming through with revolutionary reform of our NHS, which he's committed to.

Is Mr Blair too worried about his legacy?

"I think that's an important factor in the tidal wave of reform in the NHS, much of it ill-thought out, much of it reform upon reform."

Ideas have come forward which would not have seen the light of day had Mr Blair had more time to consider them, argues Mr Prentis.

The unions celebrated their 56-point pre-election deal with the government - the Warwick agreement.

The idea of this agreement was that the unions received commitments on pensions, skills, equality issues, employment rights and public services in return for supporting Labour's electoral campaign in 2005.

But Mr Prentis says there is now a "degree of collective amnesia".

"We weren't lulled into a sense of security by the Warwick Agreement," he says. "These were firm agreements that have now been ignored."

NHS demonstrations

Unison is asking the TUC to use "all means disposable" to the union movement to defend the NHS against a "competition and markets" agenda.

It has already balloted 1,000 workers on taking strike action over a deal to privatise the supply of goods and equipment to hospitals.

But he says the campaign goes far wider than the "last resort" of industrial action.

Mass regional demonstrations, lobbies of Parliament and an information campaign for MPs and the public about the dangers of privatisation are all planned.

Gordon Brown is not really left-wing, says Mr Prentis

And he thinks public support for the campaign will ensure its success.

Mr Prentis says Unison is not engaged in an ideological campaign - unlike Downing Street.

Instead, it believes that using markets just does not work and the only beneficiaries will be the multi-national private firms making profits out of taxpayers' money.

He points to the budget deficits seen this year in the NHS.

Health Secretary Patricia Hewitt has insisted the NHS's core principle of treatment free at the point of need is unchanged and using a range of providers is helping to treat patients faster and better.

But Mr Prentis warns: "If this is a model for the future, then it's going to get us nowhere because it's not based on fact, it's not based on evidence, it's so costly that hospitals will have to close, jobs will be lost despite extra money going in."

Leadership questions

Given his bleak view, one might think he would be calling for Mr Blair to quit now.

He says the uncertainty is not healthy for Labour or the government but he is not demanding a specific handover timetable.

"We have got to resolve the position of the leadership very quickly," he argues, saying it is irrelevant to him whether Mr Blair goes in February or May.

Mr Prentis says the debate over Labour's future policies gives the unions a golden opportunity to set the agenda.

That may particularly true when the new leader does emerge.

"We are not saying he or she has got to do everything we want, but we are saying we have to be listened to, otherwise whoever takes over will be like a king or queen with no clothes on," he says.

Gordon Brown is still the clear leadership favourite but Mr Prentis does not expect him to adopt the unions' demands wholesale.

It was Mr Brown, after all, who was responsible for policies like the private finance initiative.

Mr Prentis says: "We're not naive enough to believe that Gordon Brown, despite the image painted of him by some of the press as being the left wing candidate, is necessarily left-wing.

"He's not left-wing in our eyes and to label him in that way is probably unhelpful."

The TUC might be dominated by talk of leadership battles, but Unison is clearly up for the policy fight.