A Conservative donor is attempting to force a referendum on the EU reform treaty through the courts as the debate on the Lisbon treaty begins in parliament.
Stuart Wheeler, who set a record when he donated £5 million to the Conservative Party in 2001, is applying for a judicial review over the government's refusal to put the matter to the public.
At the heart of the dispute are conflicting interpretations of the contents of the Lisbon treaty. The Tories have repeatedly claimed it closely resembles the EU constitution, which was rejected by French and Dutch voters in 2005.
As the government said it would hold a referendum on the constitution in its 2005 election manifesto, Mr Wheeler believes the time has come to force the government's hand.
"This is a very serious attempt to get a referendum," he argued on this morning's Today programme.
Mr Wheeler believes parliament will not be able to ratify the treaty until the judicial review has been held.
"The first stage is to go to the court and to ask for a judicial review; we expect to get that, and once we've got it I'm told reliably parliament will not be able to ratify until the judicial review has been held," he added.
Mr Wheeler said the challenge "certainly could" hold up the existing timetable to debate and ratify the treaty through parliament.
"If we get the hearing, as I think we will, I would imagine the Labour party and the government would ask for the matter to be expedited, otherwise it would hold it up a long time," he said.
"And I'd be very pleased if it did hold it up a long time, but in any case when it is heard we have an excellent shot of winning it anyway."
MPs began debating the Lisbon treaty today after spending yesterday evening discussing how much parliamentary time should be spent on it.
In the end the government won backing for a 12-day debate by 56 votes.