British Prime Minister David Cameron warned Friday of a lack of progress during talks in Brussels on a deal to curb migrant benefits, upping the ante in the battle to keep Britain in the EU.
Cameron held a crucial meeting with European Commission chief Jean-Claude Juncker to discuss a "migration brake" that would meet his key demand -- a four-year limit before EU workers in Britain can claim welfare payments.
The negotiations to prevent a so-called "Brexit" from the 28-nation EU come amid a series of crises for the bloc including the biggest influx of migrants and refugees to Europe since World War II.
But Cameron, well known for his brinkmanship, said it would take more work to reach a deal at a crucial summit on February 18, before a referendum on Britain's membership of the European Union, probably in June.
"We have made some progress today; it's not enough, it's going to be hard work" he told Sky News television after his talks with Juncker. "There is now a proposal on the table, it is not good enough, it needs more work."
Asked about the chances of a deal when he meets his EU counterparts next month, Cameron added: "I can't be certain we'll get there in February but I will work as hard as I can to deliver a good deal for the British people."
European Parliament head Martin Schulz, who also met briefly with Cameron, said he was "optimistic there will be a deal in February" but warned that the "devil is in the detail".
The pressure is now on ahead of a dinner that Cameron will host for European Council President Donald Tusk in London on Sunday at which they will further try to hammer out details.
Tusk is expected to table his proposals for a possible British deal on Monday, European sources told AFP.
In a sign of the urgency of Friday's talks, Cameron cancelled a visit to Denmark and Sweden to hold Friday's working lunch with Juncker, the head of the EU's powerful executive, whose appointment Cameron opposed in 2014.
Many EU nations, especially those in central Europe which have many nationals working in Britain, say a benefits limit would be discriminatory and harm the bloc's core principle of freedom of movement.
Polish Foreign Minister Witold Waszczykowski was firm in his stance against any change to the welfare benefits currently enjoyed by hundreds of thousands of Polish workers in Britain.
"I want to stress that Polish authorities won't agree to the infringement of one of the EU's fundamental rights, namely its citizens' right to freedom of movement within the EU," Waszczykowski told parliament.
"We won't accept solutions that would result in discrimination against our countrymen in any EU member state."
Cameron has set out four key areas for a deal: migrant benefits, safeguards against more political integration in the EU, protection of countries that do not use the euro currency and the boosting of economic competitiveness.
The big sticking point has been Cameron's insistence that EU migrants employed in Britain must wait four years before claiming welfare payments such as tax credits or housing benefits.
A "migration brake" that would allow Britain or any other country to limit benefits to EU migrants, if it can show its welfare system is under strain, was the main option under discussion at the talks with Juncker, diplomatic sources told AFP.
Crucially it would be up to the other EU member states to decide on an application to do so -- not the European Commission, the bloc's executive arm and guardian of the bloc's treaties.
Cameron has insisted that he is in "no hurry" for a deal and will walk away if he does not get want he wants as his deadline for the referendum is not until the end of 2017.
But Cameron is also keen to get the deal through before any new flare-up in the migration crisis over summer, and before further strife erupts among the eurosceptic members of his own centre-right Conservative party, which was re-elected in May.
Former minister and leading eurosceptic John Redwood described the migration brake proposal Friday as an "insult to the United Kingdom."