EU president Donald Tusk said Monday he expects a deal at a summit in February to keep Britain in the bloc. Nevertheless, he has emphasized that EU still faces a tough challenge with UK over the demands by Prime Minister David Cameron on migrant benefits.  

"The December European Council (summit) should address all the political dilemmas related to this process. Based on a substantive political discussion we should be able to prepare a concrete proposal to be finally adopted in February," Tusk wrote in a letter to European Union leaders.

He wrote further in his letter that uncertainty over a planned referendum on Britain leaving the EU was "destabilizing" the Union. 

"Consultations have shown that the issues raised by the British prime minister are difficult. At the same time there is a strong will on the part of all sides to find solutions that respond to the British request while benefiting the European Union as a whole," he emphasized. 

Tusk further said he would act as an "honest broker" but urged leaders not to drag out the process of negotiation with UK, which will start in earnest and in person at next week's summit in Brussels on Dec. 17 and 18.

Meanwhile, Prime Minister Cameron has reportedly welcomed a signal that a strong will exists in the European Union to reach a deal with Britain over his terms for membership in the bloc. However, he has indicated that he is aware that he will have to push for a deal with EU over welfare payments for migrants.

Cameron has promised to hold a referendum on whether or not to stay in the European Union before the end of 2017 if EU fails to meet his demands.

The most problematic of the issues Tusk listed is a British proposal to deny welfare benefits to EU citizens working in Britain for the first four years they are there -- something numerous leaders and officials have said could breach EU treaty obligations not to discriminate among citizens of the bloc.

EU membership has long been a contentious topic in Britain. Eurosceptics, who believe the UK would be better off outside the political and economic union, seek the UK's withdrawal from the EU.

A survey published by The Independent last month indicated that a 52% majority of Britons favor exit from the EU.