Mr Kinnock, Roy Hattersley, his former deputy, and Gerald Kaufman, the former shadow Foreign Secretary, signed a Commons motion supporting the rapid completion of the ratification of the Maastricht treaty.
The motion, tabled by Labour backbenchers, led by Peter Mandelson, the former Labour director of communications, was signed by 85 Labour MPs - about a third of the Parliamentary Labour Party.
It was seen as a public signal to strengthen Mr Smith's resolve to reject demands by some anti-Maastricht Labour MPs to oppose the Bill. In spite of reservations about Britain's opt-out on the social chapter, there is growing support across the party for Maastricht to deliver a socialist check on Tory policies in Britain.
The motion supported the declaration calling for 'the rapid completion of the ratification of the Maastricht treaty and its implemention' made last week at a shadow summit of European socialist leaders, including Mr Smith, in Edinburgh.
The Labour leadership is unlikely to oppose the Bill on the third reading, and might refuse to support attempts by Tory and Labour rebels to delay its passage by filibusters. Some leading Labour MPs who have signed it have privately told members of the Shadow Cabinet they would break ranks and vote with the Government if Labour opposed closure motions to speed up the Bill's passage.
Labour abstained on the Bill on the second reading, and the Mandelson motion makes it more likely that Labour will do so on the third reading. That will dismay the Tory rebels who were hoping for Labour support to delay the Bill.
The Labour leadership intends to press line-by-line amendments, but privately does not expect the Government to be defeated on any of the votes during the committee stage.
The Government is expected to drive the Bill through the Commons by holding the committee stage on two days every week after the Christmas recess until it is completed.
Tony Newton, the Leader of the House, announced yesterday that the committee stage would be resumed with two days in the first week that MPs return to the Commons after their break.
Opponents of the Bill yesterday announced plans for a new year campaign for a referendum, including a march and candlelight vigil outside Downing Street.
Six Tory rebels have tabled an amendment proposing a referendum before the Bill to ratify the treaty can be implemented.
Voters would be asked 'Do you want the provisions of the European Communities (Amendment) Act 1993 to be put into effect?'.
But there is no likelihood of the Government being forced to accept a referendum as the Labour leadership also opposes the idea. Labour leaders told European colleagues in Edinburgh that a referendum in Britain would be likely to produce a 'no' vote, destroying their European socialist strategy.
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