Trump's allies, however, are fighting back - demanding transparency and suggesting that the UK wouldn't want the documents withheld unless it had something to hide. 

The Telegraph has talked to more than a dozen UK and US officials, including in American intelligence, who have revealed details about the row. 

British spy chiefs have "genuine concern" about sources being exposed if classified parts of the wiretap request were made public, according to figures familiar with discussions.

"It boils down to the exposure of people", said one US intelligence official, adding: "We don't want to reveal sources and methods." US intelligence shares the concerns of the UK. 

Another said Britain feared setting a dangerous "precedent" which could make people less likely to share information, knowing that it could one day become public. -The Telegraph