The disclosure is regarded as "completely unacceptable" by Britain, both because of the distress it may cause families of those killed or injured and because of the risk it could complicate ongoing investigations.

The row - which goes to the heart of the close intelligence-sharing relationship between the transatlantic allies - provides an awkward backdrop to the Prime Minister's meeting with President Trump at the Nato summit in Brussels.

A Whitehall source said: "We are furious. This is completely unacceptable.