UK Independence Party leader Nigel Farage described Mr Cameron's visit to Paris as "part of a softening-up process by European leaders on Britain".
Mr Farage said: "We know what Sarkozy and Merkel want - a solid fiscal debt and political union. To get this, they require a treaty change.
"Cameron, however, wants to help them but does not want a UK referendum on Europe. This meeting is about trying to square that circle."
Mr Farage said the Prime Minister should use the "once-in-a-lifetime opportunity" of the euro crisis to "act in British interests" by renegotiating UK relations with the EU.
"That he refuses suggests that he prefers the polite applause of Paris, Berlin and Brussels to the wishes of the British people," he added.