Ken Clarke has hit out hard at the increasingly bellicose anti-immigrant rhetoric coming out of Downing Street, with a description of concerns about EU freedom of movement as "typical right wing, nationalist escapism".
The broadside from the veteran europhile minister comes as David Cameron tries to face down a significant challenge on his eurosceptic flank, with a letter from 95 Tory MPs demanding parliament be given a vote on all EU laws.
The intervention from Clarke, currently Cameron's trade envoy, comes amid ever-tougher rhetoric on benefits and immigration following the ending of work restrictions on Romanians and Bulgarians on January 1st.
Cameron is even having to patch up relations with EU allies like Poland, after he repeatedly said their citizens should not be able to come to the UK and claim benefits.
But Clarke rejected Cameron's claim that free movement rules have led to "vast migrations".
He told the Financial Times: "I just don't think it's true that the European Union is responsible for unacceptable waves of migration.
"The idea that you can have some fundamental debate that somehow stops all these foreigners coming here is rather typical right wing, nationalist escapism, I think."
Conservative and Labour politicians have entered into an arms race on limiting benefits for new EU arrivals, although experts point out that any measures imposed by the UK will affect British citizens elsewhere in the continent, who are similarly able to claim benefits in their new home.
Cameron's plans of limiting benefits for the first three months is in line with EU law, according to officials.
But Iain Duncan Smith said the government was trying to prevent EU migrants claiming benefits for two years. Ukip wants a five year ban.
Britain would almost certainly face a legal challenge in the event of a more extensive benefit moratorium.
Asked whether he accepted Clarke's view that there had been no mass migration in Europe on the Today programme, foreign secretary William Hague said: "That depends on what happens in the future.
"We are in favour of people being able to move for work. People should be able to move within the EU for work, not in order to take advantage of benefits."
Meanwhile, Cameron was trying to fight off a threat from his other flank, with prominent eurosceptics in his party trying to push him towards an ever-more radical position on the EU.
William Hague roundly rejected efforts by 95 Tory MPs to force the government to change the law so parliament could veto all EU legislations.
"If national parliaments all around the EU were regularly and unilaterally able to choose which bits of EU law they would apply and which bits they wouldn’t, the European single market wouldn’t work," the foreign secretary said.
Reports suggest prominent supporters of the idea, including Bernard Jenkin, Sir Gerald Howarth, Douglas Carswell, have taken the prime ministerial snub personally, not least because of the enthusiastic participation of Nick Clegg.
The letter showed the weakness of Cameron's efforts to placate eurosceptic backbenchers in his party.
His pledge for an in/out referendum on Europe temporarily pacified his backbenchers, but the letter suggests a new showdown could come to a climax before the time of the general election in 2015.
Statistics from Romania shows net migration has actually declined significantly since 2007, when it joined the EU.
In 2012, about 170,000 people left the country, while over 167,000 returned.
On average, mobile EU citizens are more likely to be employed than nationals of the host country and often fill skills shortages.
They are also disproportionately young and active and less likely to claim benefits.