An announcement of the figure will be made later this month by the Low Pay Commission, the body set up by the Government to recommend how the manifesto commitment to a statutory floor for earnings should be implemented.
It will come as a fresh blow to the unions, already reeling from Tony Blair's determination to side with the employers over his other key pledge on trade union recognition.
TUC leaders are to meet the Prime Minister this week to discuss the long- awaited White Paper on rights at work. News of the minimum wage being set at the lowest end of expectations is bound to exacerbate relations still further.
A minimum wage set at pounds 3.60 an hour would mean around pounds 137 for a 38-hour week, or just over pounds 7,000 a year. Union experts calculate that if, as expected, a lower rate is set for workers under 21, the proposed wage would apply to only about 1.5 million employees. They also insist that it would have no effect on employment.
Rodney Bickerstaffe, general secretary of Unison, Britain's largest union, said: "Obviously, if this is the figure it would not get three cheers from millions of people who by any stretch of the imagination are low- paid. It will fall well short of both Unison's and the TUC's aspirations."
The TUC has proposed a minimum wage of pounds 4 an hour while Unison wants pounds 4.61 under a formula that would tie the rate to the movement in male average earnings. The unions had been expecting a figure closer to pounds 4.
"Everybody must welcome the fact that there is going to be a base line against which people will be able to measure exploitation, and to stop that exploitation by enforcement," said Mr Bickerstaffe. "Obviously, we will have to build on that floor over the next few years to get a decent living wage."
The Low Pay Commission's recommendation will go first to Government before a consultation exercise with both sides of industry. Proposals on the national minimum wage and rights at work will form part of the Queen's Speech in November for the next legislative session of Parliament.
On recognition, the Government is understood to be moving towards a formula requiring unions first to be able to show they have 15 per cent membership in any proposed bargaining unit. Then, in a secret ballot, they would have to secure the approval of 40 per cent of the workers involved.
Firms employing fewer than 30 workers would be exempt from the scheme, excluding six million workers from statutory trade union recognition.
Unions turn left, page 4