The German foreign ministry has summoned Britain’s ambassador in Berlin, to face questions about reports that the embassy was used as a secret listening post.
Allegations that the embassy was used to monitor Germany's seat of power were reported in The Independent, based on documents leaked by US National Security Agency (NSA) whistleblower Edward Snowden.
Officials remained stubbornly tight-lipped on the meeting between Guido Westerwelle, Germany's foreign minister, and UK Ambassador Simon McDonald. A spokeswoman for the UK embassy said she could confirm that "the meeting has taken place but we are not commenting on anything else to do with this at all."
Asked about the claims at a regular briefing in Westminster, Prime Minister David Cameron's spokesman said: "We don't comment on intelligence matters. We have an excellent relationship with the German government and I believe that will continue."
And a Foreign Office spokeswoman said in a statement: "Her Majesty's Ambassador attended a meeting with a senior official at the Ministry of Foreign Affairs at their invitation this afternoon."
And that was it.
A German foreign ministry spokesman's statement was more telling: "At the instigation of foreign minister [Guido] Westerwelle, the British ambassador was asked to an interview in the Foreign Office.
"The head of the European Department asked for a response to current reports in the British media, and pointed out that the interception of communications from the premises of a diplomatic mission would be behaviour contrary to international law."
The Independent also said an American intercept "nest" on top of its embassy was believed to have been shut down last week as the US attempted to limit the damage caused by revelations that it carried out surveillance on German chancellor Angela Merkel's mobile phone.
The NSA documents, together with aerial photographs and information on previous activities in Germany, suggest Britain is operating its own covert eavesdropping post on the embassy roof, close to the Bundestag parliament building and Merkel's offices in the Chancellery, the Independent reported.
Allegations about NSA spying overshadowed last month's European Council summit, and led to a joint call from Merkel and French president Francois Hollande for talks with the US authorities to rebuild trust.
Cameron has not spoken to Mrs Merkel about the eavesdropping allegations today and has no plans to contact her over the issue, his spokesman said.
The spokesman said that Britain's intelligence and security services operate under a "strong and clear legal framework".
At his end-of-summit press conference, Cameron refused to be drawn on whether GCHQ was spying on EU allies through its Tempora programme of internet surveillance, saying only that the agency operated within a proper legal framework.
He did emphasise that Britain shared its intelligence extensively with EU partners, and he echoed recent comments by MI5 director-general Andrew Parker condemning the way its efforts were being jeopardised by leaks.
''The point is, what Snowden is doing and, to an extent, what the newspapers are doing in helping him do what he is doing, is frankly signalling to people who mean to do us harm how to evade and avoid intelligence and surveillance and other techniques,'' he said.
''That is not going to make our world safer; it's going to make our world more dangerous. The first priority of a prime minister is to help try and keep your country safe.
''That means not having some lah-di-dah, airy-fairy view about what this all means, it's understanding intelligence and security services do an important job.
''Yes, they need to be governed under law, yes, they must be scrutinised by Parliament, but we need those people. They are brave people who help to keep us safe and I've lost count of the plots that I have seen and the problems that I have seen being avoided by the work they do.
''That is really important, not just for Britain, but the information that we gather that we then share with other countries in Europe has helped those countries in Europe too."