Britain risks losing military influence in the world and weakening the Nato alliance if it quits the European Union, a leading German politician has warned.
In an unusual intervention in a domestic political debate of a foreign country, German Defence Minister Thomas de Maiziere made clear that Berlin is concerned at the prospect of losing an ally on security issues within the EU if the UK leaves.
Prime Minister David Cameron has promised to renegotiate Britain's relations with the EU if the Conservatives win the next election and to hold a referendum on the UK's continued membership by the end of 2017.
But Mr de Maiziere said it was important that any decision on EU membership takes into account the potential damage it might do to the UK's security interests.
Speaking to The Guardian, he said: "If Great Britain leaves the EU, it would be a great disappointment to us. It would weaken Nato, it would weaken the British influence within Nato. I think from a military point of view the disadvantages for Great Britain would be bigger than the advantages.
"I am not talking about economic issues or social issues, or whether you drive on the left or the right side of the road - I am talking about security. I am talking about British influence beyond its own borders.
"I think it is part of the British tradition that Britain has to play a role in the world. Outside the EU it would not lose a role, but it would reduce their own influence and this cannot be in the interests of Great Britain.
"We in Germany would lose a strong partner for a pro-Atlantic co-operation with America and a pragmatic British way to deal with security issues."