Brussels (AFP) - Polish Prime Minister Donald Tusk, named Saturday as the next European Union president, said he could not imagine the bloc without Britain and pledged to do everything possible to meet London's demands for reform.

"No reasonable person can imagine the EU without the UK; I cannot imagine it myself," Tusk said of an increasingly eurosceptic Britain where Prime Minister David Cameron has promised a referendum on EU membership in 2017 after negotiating a return of powers to London from Brussels.

"I am sure that the future of the EU is not about making it smaller," Tusk told a press conference just after the 28 EU leaders formally appointed him to head the European Council from December.

He said he had discussed the issues with Cameron -- who had originally been very cool on Tusk's candidacy -- and he was certain that common ground could be found.

"The EU and I personally will take on the concerns voiced by the UK," he said.

"I am sure with a reasonable framework ... we can reach an agreement," he added, citing specifically freedom of movement in the EU which London claims is being abused by benefit cheats from eastern Europe.

Cameron backed Tusk after they spoke by phone earlier this week, with the British leader seeing him as a reformist counterweight to the federalist Jean-Claude Juncker, the recently named new head of the European Commission.

But Cameron was initially reluctant to see Tusk take the top job, with relations strained by a series of spats in recent months.

In June, Poland's foreign minister allegedly said Cameron's concessions to British eurosceptics showed his "incompetence in EU affairs."

Foreign Minister Radoslaw Sikorski and ex-finance minister Jacek Rostowski -- both pro-Europeans with strong British ties -- were reportedly bugged decrying Cameron's domestic strategy on the EU as a sign of weakness after eurosceptic parties made major gains in May elections.

"You know what, his whole strategy of tossing them (eurosceptics) a bone to satisfy them has, just as I predicted, turned against him," Sikorski purportedly said.