Sarkozy and German Chancellor Angela Merkel fell out with Prime Minister David Cameron at least week's EU summit, when London refused to sign up to a pact imposing closer economic coordination between member states.
"We did everything, the chancellor and I, to allow the British to take part in the agreement. But there are now clearly two Europes," Sarkozy said in an interview with the French daily Le Monde.
"One wants more solidarity between its members and more regulation. The other is attached only to the logic of the single market," he said.
But, asked whether Britain, which has refused to join the single currency and opposed last week's fiscal pact, could still remain inside the EU single market, Sarkozy said: "We need Great Britain."
"We'd be greatly impoverished if we allowed its departure which, luckily, is not on the agenda," he insisted.
Separately, the head of France's financial regulator branded Cameron's Conservatives "the stupidest" right-wing party in the world for pushing its leader into confrontation with Europe.
"It's rare to see a European country truly refuse to reach a deal because of, to put it crudely, pressure from the finance lobby," Jean-Pierre Jouyet, chairman of the AMF market regulator, told France Inter radio.
"For a long time we have thought the French right the stupidest in the world," he continued.
"I think, in this case, the British right has shown that it can be the stupidest, in that it has served not its national interest but purely the interests of high finance," he declared.
"I think that's a shame because we need our British friends in Europe," he said, arguing that Cameron's centre-left predecessors Tony Blair and Gordon Brown would not have made "the same mistake".