Spying on your friends and allies is a serious charge.
The Germans haven't made that accusation publicly.
But this afternoon the British Ambassador, as the Foreign office put it, "attended a meeting at the invitation of" the German Government.
So he wasn't "summoned" to the Foreign Ministry in Berlin, a diplomatic way of signalling real anger.
But the Germans are making a point, if not a public protest.
Simon McDonald was called in to explain the purpose of this large white, domed structure that's been on the roof of the British Embassy for thirteen years. Presumably the German Intelligence service, the renowned BND, have long known it was there and why it was there.
The allegation now is that it's there to eavesdrop on German officials; to listen to politicians' phone calls; to spy.
One suggestion is that after the United States was revealed to be bugging the phone of the German leader Angela Merkel and stopped that, Britain took over.
Now, there's no evidence that this is the case.
But, Britain is in an intelligence alliance with the US, Canada & others known as Five Eyes, which - we now know - has gathered intelligence on its European allies.
So the Germans reminded the British Ambassador today that snooping from an Embassy is illegal under International law.
They are (pardon the pun) hacked off at this.
Some German politicians are calling for a "no spying" agreement with the UK.