MI6 chiefs are secretly battling US President Donald Trump to stop him publishing classified information linked to the Russian election meddling investigation.
The UK is warning he will undermine intelligence gathering if he releases pages of an FBI application to wiretap one of his former campaign advisers.
However, the US President's allies are fighting back, demanding transparency and asking why Britain would oppose the move unless it has something to hide.
It puts the spotlight on whether the UK played a role in an FBI inquiry launched before the 2016 presidential election into Trump campaign ties to the Kremlin.
The Daily Telegraph talked to more than a dozen UK and US officials, including in US intelligence, who have revealed details about the row.