'I could back No vote' on EU, Cameron says

"If I don't achieve that, it will be for the British public to decide whether to stay in or get out".

Cameron plans to renegotiate Britain's EU status before holding an in/out referendum in 2017, assuming his Conservative Party wins next May's general election.

“I want the 27 other countries in Europe to see that there is a plan here – that can end with a reformed EU and a reformed relationship with Britain and Britain staying in", he added on Sunday.

But his hopes of keeping his party united on Europe took a blow over the weekend, when backbench MP Mark Reckless defected to the anti-EU Ukip party on the eve of the Conservative's party conference in Birmingham.

The move, the second Ukip defection in a month, means that Cameron is likely to tack to the right in a bid to prevent further MPs switching sides.

In his conference address, Cameron is to demand that governments be given more control over the EU's “freedom of movement” rules which allow EU citizens to live and work in other countries in the bloc.

He is also expected to reiterate the need to crack down on "welfare tourism".

Reckless said his decision to join Nigel Farage's Ukip was prompted by Cameron's stance on immigration and the EU. Cameron was "not serious about renegotiation", he noted.

Meanwhile, Farage has hinted that talks are ongoing between Ukip officials and a handful of MPs from the Conservative and Labour benches.

Dan Hannan, an MEP and close friend of Reckless and Douglas Carswell (who defected in August), has been widely touted as a likely target for Farage, although he has insisted that he will not leave the Conservatives.