Conservative EU champion Ken Clarke has hit out at the "extreme right-wing nationalism" of eurosceptics - in both Ukip and his own party.
Responding to comments from David Campbell-Bannerman, the former Ukip MEP who has returned to the Tory party, Clarke spoke out against the views of those who believe Britain can go it alone.
"The world of the 21st century is one in which the British are going to have some clout and are going to have some idea of how to give themselves a platform to exercise that clout," he told a fringe event organised by the ResPublica thinktank.
"This is not time for paranoia, this is no time for old-fashioned nostalgia.
"This is no time for extreme right-wing nationalism, believing that somehow we can opt out of all this and cope with it ourselves.
"That is the bigger issue that will be resolved if we can ever get this European debate finally resolved."
Clarke's comments have raised eyebrows in Manchester by grouping the "extreme" views of Ukip with others who have argued Britain could prosper outside the EU.
They include Clarke's Cabinet colleague Iain Duncan Smith, the work and pensions secretary, who last year suggested the UK could "have it all" either in or out of the EU.
Today Clarke said he felt "bewildered" that the debate about Britain's membership of the European Union is taking place at all.
His party will argue the case for an in-out referendum on Europe by the end of 2017. Foreign secretary William Hague last night said he hoped to win over Conservative voters considering voting Ukip by pointing out only the Tory majority government would be able to deliver such a choice.
But Clarke mocked the Ukip outlook as "a world in which we have to fight off the immigrants, fight off the foreigners [and] disengage from all this - proudly back to some long-lost age when apparently we didn't need to bother with all these problems".
He added: "If we allow Mr Bloom and Mr Farage to lead us off into some land of splendid isolation I must say I weep for England. The patriot in me is disturbed."
Clarke said Britain would lose out in global trade talks to emerging economies if it left the EU, warning negotiators would be "outgunned by the Americans".
"Little Britain exercising sovereignty on its own isn't going to get very far," he said.
Those arguing that Britain could prosper outside the European Union often cite Norway as an example - but Clarke cited Norway's oil resources and said its government relies on emails from Sweden to monitor developments in Brussels.