The government is being taken to court over its refusal to conduct a referendum on the new EU treaty.
Spread betting millionaire Stuart Wheeler will be in the high court later challenging the government's position.
He says the public had a "legitimate expectation" of a referendum after Tony Blair promised one on the now defunct EU constitution.
The government claims the current Lisbon treaty is qualitatively different to the old constitution, which was rejected by French and Dutch voters.
The case comes just days before Ireland - the only EU state holding a referendum on the issue - goes to the polls.
MPs approved the treaty by 346 votes to 206, but it has now gone to the Lords, where Tory and UKIP peers will fight a last ditch effort to prevent its ratification.