UK Prime Minister David Cameron has said that he was delighted that talks on the renegotiation of Britain's membership of the European Union are now underway, with London expected to present its proposal to the council in December.

Speaking to reporters in Brussels after midnight following talks with other EU leaders on Greece and the migration crisis, Cameron said: "It has been a long night and we have discussed some very important subjects, but above all I am delighted that the process of British reform and renegotiation and the referendum that we are going to hold – that process is now properly underway."

"People always say to me: 'These things aren't possible. You will never get them done. Well, once again we have proved we will get them done. We have started that process," he said, according to Reuters.

Despite Cameron's optimism, European Council President Donald Tusk was quick to point out that although there was a will to help the UK, basic values "were not for sale."

Tusk, who will be overseeing the membership negotiations, said the talks would start now but: "One thing should be clear from the very beginning: the fundamental values of the European Union are not for sale and so are non-negotiable.

"We should consider British concerns, but only in a way which will be safe for all of Europe. We'll come back to this in December," he said, according to BBC.

David Cameron
Cameron spoke to reporters in Brussels after midnight following talks with other EU leaders on Greece and the migration crisisGetty

Italy says EU without the UK is 'impossible'

According to Reuters, Italian Prime Minister Matteo Renzi, told reporters after having lunch with Cameron in Milan on Wednesday: "For us it is priority the UK can continue to work inside the European Union because a European Union without the UK is impossible."

He said later in Brussels that he agreed with the idea of a "more efficient" and "less bureaucratic" Europe. "For this reason, the battle of wills is also our fight, our goal, our commitment. We have some different ideas to those proposed by David, but tonight David simply presented his project of referendum," Renzi said, according to BBC.

"We agreed that at the council next December he will present to everyone a project for the relationship between Europe and the UK. It will be a good process."

Ireland's Minister for European Affairs Dara Murphy told BBC Radio on Wednesday that his country has started contingency planning for a British exit from the EU.

"The core focus at the moment is the strategy around the negotiation to play a part in keeping the UK in the European Union. But yes, it would be remiss of us given the possibility that our largest trading partner may be exiting the European Union, that is something we, of course are looking at," Murphy said.