A top official in Britain’s ruling coalition says conservative Prime Minister David Cameron’s decision to block European Union treaty changes aimed at protecting the euro currency is “bad for Britain.”

Deputy Prime Minister Nick Clegg said Sunday on British television that he was “bitterly disappointed” by the outcome of last week’s EU summit, during which Mr. Cameron rejected the treaty changes. Clegg’s Liberal Democrat party joined forces last year with Mr. Cameron’s euro-skeptic Conservative Party to form a power-sharing government after 13 years of Liberal Party rule.

Britain was the only nation in the 27-member union to reject treaty changes that would impose binding caps on spending and borrowing by member countries. Supporters, led by France and Germany, also wanted a unified corporate tax rate and a new financial transaction tax. But Britain, which does not use the euro, voiced concerns that the plan would undermine its sovereignty and diminish London’s role as a dominant financial center.

On Friday, Mr. Cameron said he made a “tough, but good” decision to block the EU-wide changes.

Despite coalition differences, Clegg sought on Sunday to calm speculation that Mr. Cameron’s veto could lead to a collapse of the coalition government. He said such a breakup would be a “disaster” far worse than the prime minister’s rejection of treaty changes.