Demands for a public vote on the EU Treaty are due to be given fresh impetus with the launch of an official cross-party referendum campaign.
MPs from the three main parties, including Labour former ministers Kate Hoey, Frank Field and Graham Stringer are backing the "I Want a Referendum" drive, which is chaired by Derek Scott, vice-chairman of Eurosceptic pressure group Open Europe.
Labour MP Gisela Stuart, who was among the EU group which drafted the original constitution, has also signed up, along with Tory MPs Michael Gove, Nick Herbert, David Heathcoat-Amory and Greg Hands, and Liberal Democrat Mike Hancock.
The group's website, www.iwantareferendum.com, is due to go live as part of a nationwide campaign backed by local campaigns in every region during September and October and a cinema advert later this month.
Mr Scott said: "In the coming months we will be increasing the pressure on the Government not to break its promise to hold a referendum on the constitutional treaty.
"We will be building a broad-based campaign in every part of the country."
Ms Stuart added: "This is an issue of trust. We were elected on the promise of a referendum. If we are serious about restoring trust in politics we have to keep our promise and give people a say on this important decision."
Prime Minister Gordon Brown is under mounting pressure from both Eurosceptic and pro-European MPs to hold a poll rather than push the deal through Parliament.
Up to 120 Labour MPs are reported to support calls for a referendum and some unions are set to table motions at next week's TUC annual conference demanding a public vote.
The PM has sought to quell fears over the treaty by pledging not to allow the deal to be beefed up during final negotiations.
