LONDON — A British vote to exit the European Union would undermine its ability to be a diplomatic player on the world stage and could damage its military capabilities, according to a respected defense policy researcher.

Britain would likely remain a significant military power if it withdrew from the European Union but that would depend on it avoiding any economic fallout from the move, according to Daniel Keohane, a senior researcher at the Center for Security Studies in Zurich, Switzerland.

The Conservative government in London has committed to a referendum on whether to remain a member of the EU by the end of next year, and Prime Minister David Cameron is trying to renegotiate the terms of British membership with other member states.

"The shadow of a British exit from the EU hangs over British international ambitions. In the worst-case Brexit scenario, the UK would probably remain a significant military power, depending on the economic fallout, but it would certainly become a much diminished diplomatic player," Keohane said in a Tuesday paper released by Carnegie Europe reviewing the recent UK strategic defense and security policy (SDSR).

Withdrawal wouldn't be just a setback for British foreign policy ambitions but would hit the EU as well, he warned.

"Brexit would greatly damage the EU's already struggling defense policy and by extension, its foreign policy. ... Worse, Brexit could also further harm the credibility of the whole EU project," said Keohane

British Defence Secretary Michael Fallon told reporters in a visit to Washington last month that withdrawal would not impact the country's defense capabilities.

"There is no direct implication for our defense because that really rests on our membership in NATO. There are some EU missions in Africa and there is the European Defence Agency that does some common procurement, but there are no real implications for defense or our defense budget," he said.

Keohane said the 2015 SDSR was more coherent and ambitious than the previous review in 2010 and showed a desire to work more closely with international partners in Europe and beyond.

"The main political message that emerges from the new defense review is that Britain is back as a serious military power," he said.

"The British are widely admired for their irony. But, it would be painfully ironic for Britain to make itself less geopolitically relevant at the very moment it wants to become more strategically ambitious," he said.

Jen Judson in Washington contributed to this report.

Andrew Chuter is the United Kingdom correspondent for Defense News.

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