EU plans to make it easier for Turkish nationals to get visas to travel to Europe, in return for Ankara's help in stemming the flow of Syrian refugees, have been denounced as "madness" by Ukip leader Nigel Farage.
A summit of EU leaders including David Cameron in Brussels agreed an action plan with Turkey which help out the prospect of an "acceleration" of moves towards visa liberalisation and a renewed drive on talks about joining the 28-nation bloc, as well as "substantial" EU financial assistance.
The plan puts no figure on the EU funds on offer, but German Chancellor Angela Merkel was quoted as saying that the figure of 3 billion euro (£2.2 billion) had been discussed and seemed reasonable.
Speaking after the conclusion of the one-day summit in the early hours of the morning, European Council president Donald Tusk voiced "cautious optimism" about the plan, which he described as a "major step" towards reducing numbers of Syrian refugees reaching Europe.
But he said any liberalisation would depend on "a responsible and adequate response from the Turkish side" in terms of reducing numbers of migrants.
"An agreement with Turkey makes sense only if it effectively contains the flow of refugees," said Mr Tusk.
Up to 2 million Syrians are living in refugee camps in Turkey after fleeing fighting in their neighbouring homeland, and the summer saw growing numbers attempting to move on into Europe - often by perilous boat journeys across the Aegean Sea to Greece.
Mr Farage said: "This Commission proposal is bordering on insanity. Agreeing to liberalise border requirements for 75 million Turkish nationals is a form of EU madness.
"From a cost, security and cultural perspective, this is completely the wrong move. If Cameron and Co allow this to happen it's the British people who will be the turkeys at Christmas. Yet another reason to leave the EU."
European Commission president Jean-Claude Juncker stressed that any moves towards visa liberalisation would not mean free entry into the EU for all Turks.
Mr Juncker said: "We have agreed with our Turkish partners that the visa liberalisation process will be accelerated. This does not mean that we would step away from the basic criteria, which are the rules in that domain. There will be no other criteria for Turkey and we will assess progress in Spring 2016.
"We are establishing a link between the delivery of Turkey as far as migration is concerned and the visa issues."
Mr Tusk added: "We need a responsible and adequate response from the Turkish side. As with any other partners in the crisis, the 'more-for-more' principle must apply. You help us, we help you - it's that simple."