UNION leaders turned up the heat on the Government last night as Alan Milburn quickly discovered how tough his new job is going to be.

On the eve of their annual conference, the unions issued an unprecedented warning to the Darlington MP that he must curb his "wild ideas".

Mr Milburn was surprisingly brought back into the Cabinet last week by Tony Blair only 15 months after stepping down to spend more time with his family.

The former Health Secretary, and noted Blairite, has been given the job of preparing Labour's manifesto for the General Election, expected next May.

And last night, unions feared Mr Milburn would be keen on modernising public services through privatisations.

The warning to Mr Milburn, outlined in a joint Press conference held by the TGWU, Unison, Amicus and the GMB, shows how worried unions are about the direction of the Labour Government.

The biggest strike by civil servants in more than a decade was on the cards last night as the Public and Commercial Services Union said it would ballot 290,000 workers, ranging from coastguards and immigration officers to prison staff and pensions advisors.

The strike, pencilled in for November 5, is against Chancellor Gordon Brown's plans to cut 104,000 civil service jobs. Other union leaders warned of further industrial action to protest against plans to extend the retirement age and the looming pensions "disaster".

In June, at the National Policy Forum, the Labour leadership and the unions came to a broad agreement about future policy - an agreement that prevented the unions for stopping their substantial donations to the party.

But the danger for Labour must now be that that agreement might not hold.

TGWU leader Tony Woodley said: "Mr Milburn, I'm told, has been brought in to have a look at the manifesto.

"He can write it, but I hope he doesn't start to rewrite it. That would be absolutely disastrous at this stage.

"Further privatisation of the health service and things like that aren't going to get activists active and they are not going to get the voters voting."

Unison, the health workers' union, is worried about Mr Milburn's "wild ideas".

It clashed with him over his flagship foundation hospitals policy, and its leader Dave Prentis said: "He has to realise that he is leading a team including trade unions and we have a legitimate voice."

The extent of the unions' concern will become clear today as Mr Blair addresses the conference in Brighton.

The GMB will tell Mr Blair to "get a grip" on manufacturing. Its research shows that 2,300 manufacturing jobs were lost last month, including 73 in Mr Blair's Sedgefield constituency in County Durham.

GMB leader Kevin Curran said: "There is an answer - state aid and intervention, investment in manual skills for the many, not just educating the minds of the few," he said.

There was some support for Mr Milburn from his close friend and Tyneside MP Stephen Byers.

He said: "There is a role for the private sector delivering public services, but it has got to be the private sector working for the public services in the public interest."