They are limbering up for a costly court challenge all the way to the House of Lords. There are even suggestions that they will contest next year's European elections on an anti-federalist platform.
Over the past year, about 40 sympathetic MPs, 26 of them 'hard-core', have been marshalled into a highly organised, well briefed, coherent force by Bill Cash, the MP for Stafford. In its ongoing battle with the Government, the group has displayed passion, ability and, crucially, financial muscle.
Since last November, Mr Cash and his cohorts have conducted business from an elegant, four-storey town house in Great College Street, a few hundred yards from the Palace of Westminster. The operation - involving the most detailed of briefing packs for MPs and campaigning in Britain and Europe - is as elaborate as the decor is opulent. Its efforts are co-ordinated with the Mayfair office of the all-party Maastricht Referendum Campaign.
The aim, Mr Cash explained, was to compete with the Government's enormous resources. 'It's like a cottage industry of expertise from all parts of the country - from universities, from lawyers, from the City.'
There is no shortage of funds. 'We have very kind benefactors,' said William Sitwell, a 23-year-old Old Etonian who handles Mr Cash's media relations.
The house in Great College Street, used as an office by Margaret Thatcher after she was ousted from office, was loaned to Mr Cash by Lord McAlpine, a former Conservative Party treasurer. Lord McAlpine sold it two months ago, but the new owners appear to be extending the hospitality.
Those 'very kind benefactors' also furnish the fax machines, computers and telephone lines. The staff are all volunteers, as are most of the clutch of lawyers, bankers and businessmen who act as outside consultants.
Donors' identities remain closely guarded. But one Tory MP speculated: 'Turn over the stones and the usual names come creeping out - Alfred Sherman, David Hart, Lord McAlpine, James Goldsmith.'
Mr Sherman, co-founder of the right-wing think tank, the Centre for Policy Studies, was baffled by the suggestion he was a donor. Lord McAlpine insisted that he had offered nothing more than the office space - though at an estimated pounds 20 a square foot, that is not ungenerous.
There is little doubt that Sir James Goldsmith, valued last year at pounds 700m, enjoys the means. The Anglo-French businessman has long argued the case for Europe, but vigourously opposes Maastricht.Reuse content