Ministers have been given confidential legal advice that John Major has the power to ratify the treaty in its present form whether or not the Government defeats a Labour amendment aimed at forcing it to reverse its hard-won opt-out from the Chapter.
The new legal opinion will provide ministers with a new weapon in their battle to contain a revolt by backbenchers when the vote is taken in up to two months' time.
Senior ministers are cautiously optimistic they will win. But a defeat would require only 12 Tories to vote for the amendment if the Ulster Unionists joined Labour and the Liberal Democrats in the 'yes' lobby. The legal advice on the outcome of a defeat, in domestic and international law, is conflicting and ministers will continue to discuss the issue with lawyers over the next few weeks.
One senior minister said it was 'a legal thicket'. Another admitted that any legal advice, however expert, was only opinion until tested in the courts.
Ratification in the face of a parliamentary defeat would provoke a serious constitutional row. It would certainly be considered only as a last resort by senior ministers now examining various options for dealing with what would anyway be a highly damaging defeat in the committee stage of the Maastricht Bill.
But the advice, which has been discussed by senior ministers, including the Attorney-General, Sir Nicholas Lyell, could be used to underpin a warning to potential rebels that they might be wasting their political careers to no purpose if they voted with Labour's amendment 27.
The amendment seeks to delete the protocol which sets a new framework for laying down minimum standards of worker protection for 11 EC countries while specifically excluding Britain from its provisions. Several options remain open if the amendment is passed, including the use of a confidence motion that endorses Britain's opt-out from the Social Chapter.
The Government could also use the Tory majority in the Lords to reverse the amendment, though that would have to be ratified subsequently in the Commons itself.
But ministers appear to have moderated their earlier warnings that a defeat for the amendment would lead to the collapse of the treaty.
After a meeting with the Prime Minister and the Chief Whip, Richard Ryder, on Wednesday morning, Douglas Hurd, the Foreign Secretary, said more than once in a BBC interview that the Government did not plan to ratify a treaty other than the one it signed in Maastricht.
He did not make any explicit threat to abandon the treaty if the amendment was passed, saying instead that Britain had no intention of signing up to the Social Chapter.
Lord Tebbit, who advised rebel backbenchers last week to vote for the Labour amendment to stop the treaty, told the Independent on Sunday that if the Labour amendment fell in the Commons, he would reintroduce it in the Lords.
Separate legal advice has been taken on the effect of amendment 27 on other European countries, with some ministers convinced that it would prevent any EC government implementing the Social Chapter, while at the same time leaving the rest of treaty intact.
If true, that would give the Government a powerful propaganda weapon against the Labour Party which it could then claim had torpedoed the commitment of the other 11 EC countries to fresh social EC legislation.
The legal arguments for ratifying despite a Commons defeat on amendment 27 appear to turn on two key principles. One is a view by constitutional lawyers that the power to bind in international law is a matter for the Crown and not for Parliament.
The other is that Parliament only has to give its assent to measures in the treaty which have to be incorporated in British law. That does not apply to the social protocol which explicitly has no such application.
One EC view is also that British parliamentary ratification of the social protocol is not necessary because it does not amend the Treaty of Rome, unlike other parts of the Maastricht treaty.Reuse content