John Stevens and Brendan Donnelly, who left the Conservative party last month in protest at Mr Hague's negative stance towards Europe, will seek to register the Pro-Euro Conservative party as an official political body.
They want to split the mainstream Tory party by attracting those members opposed to Mr Hague's Euro-sceptic views.
"All we are doing is what the sceptics did before us - they strong-armed the Conservative party in the most brutal way," said Mr Stevens, leader of the new party. "The pro-Europeans were herbivores then, whereas the Euro-sceptics were carnivores. Now we are going to have a real fight. I am not interested in gestures. I am interested in dealing a serious blow."
The two MEPs, who will be funded personally by Mr Stevens, a millionaire former currency dealer, intend to field candidates against the official Conservatives in the European parliamentary elections in June.
They have the backing of Paul Howell, who was a speech writer for Baroness Thatcher and Sir Edward Heath and a Tory member of the European Parliament from 1979-1994.
"It is not me who has changed my views on Europe. It is the Conservative party which changed its views," said Mr Howell. "The situation saddens me very much. I will stand against the Conservative party willingly."
The dissident Tory MEPs have not ruled out fielding a candidate in the elections for the new London assembly or the forthcoming general election. But they are expected to stop campaigning if the Conservative party abandons its Euro-sceptic stance.
Most Europhile Conservatives opposed to Mr Hague's commitment to stay out of a European single currency say they would not join the rebel MEPs because they want to influence change from within. Instead, they favour a leadership bid by the former Chancellor, Kenneth Clarke, who is in favour of closer links with other EU countries.
"I don't think Kenneth Clarke should be ruled out for the leadership if things go horribly wrong for Hague," said one Tory MEP. "We are waiting to see what happens. If Clarke was leader the whole Euro-sceptic episode could be shelved."
Last week Mr Stevens commissioned a MORI poll which suggested that a breakaway party could gain 11 per cent of the vote in the forthcoming Euro-election. The survey also indicated that support for the Conservatives could slump to 17 per cent in the June poll.
The breakaway party may also decide to field candidates under the banner "European party" - a name which it will also register this week.
Tory Central Office is considering mounting a legal challenge to the registration of a rival name but is thought unlikely to pursue the matter in the courts. It is still possible, however, that the official Registrar of Political Parties will refuse to accept the name, because of the potential for confusion with the "official" Tories.
"The formation of the party is a big step towards contesting the European elections," said Mr Donnelly MEP. "When these formalities are out of the way we can concentrate on winning support and raising funds."