Mr Cameron faces the prospect of an awkward Commons vote when MPs debate calls for a referendum. Coverage has tended to focus on the prospect of a battle between the Prime Minister and eurosceptic Tory MPs.

But it's largely the work of Ms Sinclaire (Ind West Midlands), after she led a successful campaign to collect 100,000 signatures for a petition "to allow the British people a referendum on the United Kingdom's continued membership of the European Union.".

She ambushed the Prime Minister when she bumped into him by chance at Manchester's Hilton hotel. As well as getting a photo, Ms Sinclaire reports that they had a good chat about the EU - and he was extremely charming.

She said: "He didn't want to talk about a referendum but he said he believed membership of the European Union was good for the UK."

The coalition agreement, drawn up by the Conservatives and Liberal Democrats last year, promises that any petition securing 100,000 signatures will be considered for a formal debate in Parliament.

And Ms Sinclaire and allies have collected more than 100,000 names, including 49,000 in the West Midlands alone, after she took her EU battle bus decorated with the vivid colours of the union flag across the country.

The formal request for a debate was then made by Conservative MP David Nuttall, who told the Commons Backbench Business Committee: "I suggest that the matter is of enormous national interest".

A debate is expected to be held before Christmas - with a vote on a motion to hold a referendum. However, even if the vote is passed the Government may well decide to ignore it.