LONDON - Prime Minister David Cameron on Sunday warned that quitting the European Union was "not the right answer" to Britain's problems, but that he would "do everything to make that work" if the country voted to leave.
Cameron told BBC's Andrew Marr Show he was "close" to agreeing deals to reform the union, and was open to alternative solutions to the sticky issue of welfare payments to migrants from the EU, which he wants to tighten.
The prime minister said his proposal of a four-year ban for migrants for top-up benefits for low-paid work was "still on the table" but he could agree to an "equally powerful" plan to tackle so-called benefit tourism.
"We have a welfare system, unlike many in Europe, that you have immediate access to and it is that that creates many of the difficulties," he explained.
The British premier said he was optimistic of securing a deal at an EU summit in February, and that an in/out referendum - promised by the end of 2017 - could take place soon after.
However, he said that the vote could be pushed back if he failed to secure satisfactory concessions from Brussels.
"I have to have this referendum by the end of 2017," he said. "If I can't get the right deal in February I will wait and I will keep going." Assuming agreements are reached, Cameron will campaign to stay in the union, saying "I don't think that (leaving) is the right answer." Asked whether officials had plans for a "Brexit", Cameron said "we would need to do everything necessary to make that work", but did not reveal if any contingencies had been made, angering those campaigning to leave.
"David Cameron's lack of a plan for withdrawal tells the EU - and voters - that he has no intention of leaving, guaranteeing that the deal he does finally produce won't be worth the paper it's written on," said Arron Banks, co-founder of the Leave.EU campaign.
A "Brexit" would be a huge blow to Cameron's reputation, but the prime minister again declared his intention to stay on, whatever the result, saying the referendum was not about "this politician's future or that politician's future".
Recent polls have shown growing momentum for those wanting to leave, although bookmakers still have a "stay" vote as narrow favourite.
Cameron last week met with leaders from Germany, Hungary and the Netherlands as he swung through Europe as part of his diplomatic efforts to secure a deal.