James Wharton told MPs today that the European Union is a "fundamentally different creature" to the one it was in 1975 and that the British people deserve a say on whether the UK remains a member or not.
The House of Commons is hosting a debate on Wharton's private member's bill to force an in-out EU referendum by 2017 (watch live here).
While Labour leader Ed Miliband refused to show up to the debate, it was clear there a few dissenting voices from within his party. Labour MP for Birkenhead Frank Field said a referendum was in "interests of whole of Europe to renegotiate", while MP for Vauxhall Kate Hoey said a "majority of Labour voters want a referendum". Kelvin Hopkins, Labour MP for Luton North, gave his full support.
Wharton played on the divisions well, saying he was optimistic that a "substantial portion" of the Labour party wanted a referendum, and saying he was grateful for any crossparty support.
Wharton was keen to make it clear he was not asking for a vote on whether the UK should remain in the EU or not (although that didn't stop debate along those lines), but that it should be a decision for the British people. Opponents claimed that the mere prospect of a referendum would be enough to create uncertainty among businesses.
Notably, shadow foreign secretary Danny Alexander avoided saying that Labour will never change their views on a referendum, even before the election in 2015. A leaked briefing from the Labour party (published by blogger Guido Fawkes here) said that, if there is a proposal for significant transfer of powers from Britain to Brussels, then that should be decided by a referendum.
At present, however, the official Labour line is that a bill now would not be in the national interest and that Cameron's endorsement was a sign of desperation rather than trust in the British people.
The roots of David Cameron’s approach lie much more in the politics of the Conservative Party, than in foreign policy.
For David Cameron’s backbenchers this is all about exit and they won’t give up until he gives in.
This latest step has more to do with trying to get his Party back in line rather than getting the economy back on track.
The real tragedy is that David Cameron’s Party won’t let him address the undoubted need for change in the EU in a sensible way.
Labour MP for Southampton Itcham John Denham said that the real driver behind Cameron's backing of today's bill was a fear of the rise of UKIP. The latest YouGov poll shows 31 per cent of those surveyed would vote Conservative - compared to 39 per cent for Labour, 12 per cent for UKIP and 11 per cent for the Liberal Democrats.
However, a poll by Survation puts UKIP at just one percentage point behind the Tories (at a respective 22 and 23 per cent, compared to 36 per cent for Labour and ten per cent for the Liberal Democrats).
Here's how voters' attitudes towards EU membership has changed since September 2011: