THE PRIME concern of many MPs as they arrived at Westminster yesterday was whether the Commons was heading for a weekend sitting on the Maastricht treaty legislation, writes Anthony Bevins.

That was the threat that had been circulated by the Government Whips this week. But in spite of the hysteria, it did not bear close analysis.

As the Independent disclosed yesterday, the Government does not have a natural majority for the European Communities (Amendment) Bill, with 45 Conservative backbenchers who have supported it in fewer than half of the 23 votes that have taken place so far during the legislation's three-month Committee Stage.

But that does not mean that it cannot win a vote - at some point - to sit all Thursday night and through to the normal 3pm close of business on a Friday, gaining an extra day for the Bill.

The key to that would be the support of 19 of the 20 Liberal Democrats, who voted with the Government in the paving debate on 4 November. To stage such a morale-boosting marathon sitting, the Government would have to win a technical vote to suspend 10pm rule under which business usually finishes at 10pm.

Since the Committee Stage of the Maastricht Bill began last December, there have been three votes to suspend the 10pm rule. The Government won the first one on Monday, 18 January, by 304 votes to 271, a majority of 33 - even though 31 Conservatives voted against, and a further 13 abstained.

Altogether, there were 32 Labour MPs absent for that night's vote, along with 20 minority party members and three Liberal Democrats. But 17 Liberal Democrats voted with the Government.

The Liberal Democrats again supported suspension of the 10pm rule on Thursday, 28 January, which the Government won with a majority of 47 - even though 21 Conservatives voted against and another 24 abstained - and again on Thursday, 25 February, when the Government got a majority of 26 in spite of 21 Tories voting against and 22 abstaining.

Although the House sat until 7.31am on Tuesday 19 January, having considered the Maastricht Bill all night, it finished with it at 12.58am on Friday 29 January, and at 11.17pm on Thursday, 25 February. That is not to say, however, that a 22- hour session - starting at about 4.30pm on a Thursday and going through to about 2.30pm on a Friday - is out of the question. A point might well come at which the Liberal Democrats could support such a ploy.

But as one senior Liberal Democrat pointed out yesterday, that would not be the same as the 'weekend sitting' threatened so glibly by the Government whips.

There was no question of the Liberal Democrats supporting a Government move to sit through to Saturday, never mind Sunday - even if ministers offered to introduce some form of proportional representation for the UK's six extra European Parliament seats.