Angela Merkel has given David Cameron an ultimatum over his intransigence on European Union freedom of movement, warning that Britain is fast reaching "the point of no return" when it comes to exiting the union.
Der Spiegel news magazine quoted sources within the German chancellor's office and German foreign ministry as saying that Merkel made clear she will withdraw her support for Britain's continued EU membership if Cameron insists on pressing for measures which would undermine the principle of the free movement of labour.
At a recent summit in Brussels, Merkel is said to have made it abundantly clear Germany would not accept any tinkering or redrawing of freedom of movement principles, bluntly telling him: “That’s it.” It should, Der Spiegel noted, "have left the British Prime Minister in no doubt".
The Prime Minister, who is under pressure to tighten Britain's immigration controls to counter the rise of Ukip, has already torn up one proposal to impose quotas on low-skilled EU migrants in the face of German opposition, according to The Sunday Times.
The newspaper said that Cameron was now looking at plan to stretch the EU rules "to their limits" in order to ban migrants who do not have job and to deport those who are unable to support themselves after three months.
The Prime Minister was said to want to be able to present a "German-compliant" plan to re-negotiate the terms of Britain's membership ahead of the Conservatives' promised in/out referendum by the end of 2017.
Downing Street would not comment on the reports, but did not deny that they had taken place.
A Downing Street spokesman said: "The Prime Minister will do what is right for Britain, as he has repeatedly made clear."
Cameron is under pressure on both sides of the channel, heighted by the imminent Rochester by-election likely to be won by Ukip defector Mark Reckless. But he also faces a haranguing from some colleagues. Arch pro-European former cabinet minister Ken Clarke who dismissed Ukip as an "extreme right-wing protest party" and said that free movement of labour was "absolutely essential" to the working of the single market.
"If you're going to have a sensible single market, if we want to compete with the Americans and the Chinese and so on and modern world, we need the free movement of labour," he told BBC1's Sunday Politics.
"All our companies, multinational companies, will go spare if you start inferring with that."