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But William Hague, Britain’s foreign secretary and a member of the Conservative Party, disputed Mr. Clegg’s account, saying Sunday that the deputy prime minister had been on board with the government’s negotiating position ahead of the EU summit.

“We are not marginalized, I can assure you of that,” Mr. Hague told Sky News. “Our agreement is required in the EU to a whole range of other decisions that will be coming up over the next few months.”

Mr. Cameron rejected the invitation to join 26 other EU members in approving changes to the bloc treaty in a move that isolated Mr. Cameron from the bloc and raised doubts about whether Britain realistically can remain an EU member.

Conservative lawmakers already have toasted Mr. Cameron’s decision in Brussels, while other Liberal Democrats have criticized it.

On Sunday, Mr. Clegg suggested Mr. Cameron is hamstrung by the Conservative euro-skeptics, saying, “Of course things would have been different” if he had attended the EU summit, too. “I’m not under the same constraints from my parliamentary party that clearly David Cameron is,” Mr. Clegg said.

But the deputy prime minister dismissed talk of a breakup of the coalition government.

“It would be even more damaging for us as a country if the coalition government was to fall apart,” he said. “That would cause economic disaster for the country at a time of great economic uncertainty.”

Still, Mr.  Clegg did not shy away from rebuking the stance of his Conservative coalition partners, who have called for a public referendum on Britain’s relationship with Europe and had urged Mr. Cameron to not give in at the summit.

“There’s nothing bulldog about Britain hovering somewhere in the mid-Atlantic, not standing tall in Europe, not being taken seriously in Washington,” Mr. Clegg said.

Conservative lawmaker Mark Pritchard struck back, accusing Mr. Clegg and his party of being “totally out of step” with public euro-skepticism.

“Better to be a British bulldog than a Brussels poodle,” Mr. Pritchard said.