The rebels claim their numbers have increased since a recent Commons motion, which attracted 70 signatures, called for a fresh start on economic policy following the withdrawal of sterling from the exchange rate mechanism.
Michael Spicer, a former minister, who led the list, said: 'The 70 could be the tip of the iceberg.' Kenneth Baker, the former Home Secretary, has led other senior Tory backbenchers in throwing their weight against Maastricht. He said: 'In its present form, it is not credible. The virtual collapse of the ERM tore a ragged hole in the centre of Maastricht.'
Whips believe they can reduce the size of any rebellion. They are targeting the names on two early-day motions - numbers 549 and 174 - each opposing progress on the Maastricht treaty, and put down after the Danish referendum. They will begin systematically tackling the hit-list when MPs return to the Commons on 19 October. They will concentrate on backbenchers they believe will fall into line.
The whips' priority will be 15 Tory MPs who signed the second motion opposing fixed exchange rates. These include two senior Tory backbenchers, Sir Gerard Vaughan and Marion Roe, recently made chairwoman of the Select Committee on Health.
Others include Gary Waller, who said yesterday he would support the bill if the Government returned from the Birmingham summit with a protocol on subsidiarity. 'I think most of them are like myself and want to see what comes from this summit.'
The whips will also speak to 22 Tory MPs, who signed the first motion but not the second. These include many of the new intake, such as David Willetts, Charles Hendry and David Lidington, who were ministerial advisers and members of the 'Standard Bearers'. Alan Duncan, who signed both motions, will also be targeted.
A total of 22 Tories voted against the bill on the second reading. Led by Mr Spicer, MP for Worcestershire South, they represent the hard core of the rebels and the 'Fresh Start' group, which was behind both motions.
The group plotted its rebellion at a dinner at the Carlton Club, and held occasional dinners at Rodin's in the Millbank Centre. It is likely there will be more dinners before the rebellion is over.
Yesterday, the leaders of the group were 'networking' by telephone, preparing for their show of strength at next week's Conservative party conference.
But the whips, led by Richard Ryder, the Government chief whip, will be matching their work. For Mr Ryder, the vote represents one of his biggest challenges. The whips wear a tie with a whip motif, but the penalties they wield are limited. Mr Ryder, in spite of his shy manner, is capable of giving his recalcitrant backbenchers a severe dressing down.
The 'enforcers' in the whips' office include David Lightbown, a burly northerner, jokingly called the 'caring whip', and David Davis. But they cannot use the ultimate deterrent - removal of the Tory whip. Like a nuclear device, with a majority of only 21, it would bring about self-destruction.
The Labour Party's repeated commitment not to vote against the Maastricht bill, will have persuaded the Prime Minister he has a majority to crush the rebellion. However, Mr Major and his chief whip will be on a knife edge until the last vote, on whether Labour keeps its word.Reuse content