Prime Minister David Cameron was to meet EU president Donald Tusk at Downing Street on Sunday as negotiations reach a decisive point ahead of a referendum on whether Britain should leave the bloc.

The working dinner comes with Tusk expected to publish draft proposals early this week on how to reform Britain's relationship with the EU, which Cameron can then use to campaign against a so-called "Brexit".

British officials hope that a final deal can be nailed down at a Brussels summit being held on February 18 and 19. That could then open the door to a referendum in June.

But Cameron insists he is willing to hold out for as long as it takes to secure the right package of reforms, if necessary delaying the referendum until September or even next year.

Opinion polls currently suggest that Britons would vote to leave the EU by a small margin.

Tusk's visit comes after Cameron held a hastily-arranged meeting with European Commission chief Jean-Claude Juncker on Friday to try to resolve the British leader's main concern - reducing the number of EU migrants coming to Britain.

Tusk arrived in London on Sunday afternoon accompanied by his full negotiation team, an EU source told AFP.

"I don't expect Tusk to offer future treaty change on free movement" of people, the source said.

'Thin gruel'  

Cameron wants to be able to use an "emergency brake" to curb the amount of benefits payments which migrants can claim.

"The Prime Minister will tell Tusk tonight that an emergency brake on in-work benefits would have to apply immediately," said a senior British government source.

"What form an emergency brake takes is set to be the main issue at tonight's dinner.

"The Prime Minister intends to leave Tusk in no doubt that he will not do a deal at any price," added the source.

Cameron emerged from the talks with Juncker saying that, while there had been "progress", the proposal on the table was "not good enough".

He will add that the current "emergency brake" proposal does not go far enough and that it should only be a stop gap to a more permanent mechanism.

Cameron has set out four areas in which he wants reform - migrant benefits, safeguards against more political integration in the EU, protection of countries such as Britain which do not use the euro currency and boosting economic competitiveness.

The main sticking point has been Cameron's insistence that EU migrants employed in Britain must wait four years before claiming certain welfare payments, which could require a treaty change.

Cameron is under increasing pressure from his own centre-right Conservative party, which has a strong eurosceptic contingent, to come back with a robust deal.

The right-wing Daily Telegraph newspaper called what was currently on offer "pretty thin gruel" in an editorial on Saturday.

"If Europe does not give more ground, then Mr Cameron will be taking back a deal to Britain that some may judge is full of empty gestures, jeopardising the pro-EU campaign," it added.