TRADE unions' hostility to the Government's plans to reform their movement could be greatly defused after it emerged last night that the Prime Minister was willing to give them the right to secure automatic recognition if 50% or more of the bargaining unit are members.

As final details were hammered out yesterday in an intensive round of meetings before the White Paper on Fairness at Work goes to the Cabinet, it was learned that ''a robust package'' which should largely please the unions had been negotiated behind the scenes.

In the White Paper, which is understood to recognise the emblematic importance of trade unions in the Labour movement, the unions will secure automatic recognition, without a ballot, if more than half of the bargaining unit are members.

In another critical element, there is a commitment to carry out an independent review of the proposed procedure on union recognition 12 months after it is introduced.

The White Paper will entitle every trade unionist to be represented by an external union official in a grievance or disciplinary procedure, whether the union is recognised by the employers or not.

As the trade union group of Labour MPs last night repeated its hostility to a 40% threshold before recognition, there was speculation that Mr Blair would not lower the threshold because it could be interpreted as a retreat.

But a spokesman stressed yesterday that no-one who had the authority of the Prime Minister had ever confirmed in briefings that a 40% threshold had been accepted by Mr Blair. He insisted the Government would fulfil its pledge to introduce statutory union recognition and that would be a ''big step''.

While the trade unions will be dismayed that there is no shift on the threshold, they are expected to be pleased at the White Paper in its entirety, which has been described as ''a very robust package'' for trade unionism.

They are also expected to welcome the Government's plans to maximise the turn-out by preferring workplace rather than postal ballots.

The review would examine whether to continue with the 40% requirement, and probably discard it if it is not proving effective.

The Confederation of British Industry was understood to favour a trigger mechanism that would require 30% of the employees in bargaining units to request a recognition ballot before one could be held, but the White Paper is likely to state that no trigger will be necessary.

The Government has also conceded the case for greater trade union representation within small companies. Only companies employing fewer than 20 workers will be exempt from the planned recognition procedures.

The White Paper will include wide-ranging reforms which are intended to benefit all employees. They will include new parental and maternity rights, lifting the cash compensation for unfair dismissal, and allowing the unfair dismissal legislation to apply after one year rather than two.

Over 100 Labour MPs met John Monks, the TUC's general secretary, Roger Lyons of the MSF, and Tony Dubbins of the GPMU, at the House of Commons last night.

They agreed they would issue a joint response with the TUC to the White Paper when it was published in the week after next. They will then jointly work on amendments which they hope will improve the White Paper.

A spokesman for the trade union group of MPs said they had impressed on the union leaders the importance of the package in the run-up to the elections for a Scottish Parliament.

Ken Cameron, general secretary of the Fire Brigades Union, said setting a 40% threshold would be ''unfair'' to unions. ''I don't understand why the trade union movement have to jump through hoops in order to satisfy the CBI.''

Rodney Bickerstaffe, general secretary of Unison, said he believed there would be ''a more level playing field at work'' after 18 years of serial attacks.

Jimmy Reid Page 19