Joe Biden received unredacted intelligence reports that eventually led to the prosecution of the national security adviser Michael Flynn, it emerged last night, boosting President Trump’s hopes of thrusting the case to the centre of the election campaign.

Richard Grenell, the president’s acting intelligence chief, declassified a list of government figures who asked to be told the name of a US citizen whose communications with the Russian ambassador were picked up by US intelligence monitoring the embassy in 2016.

Under US law, the names of Americans picked up incidentally during espionage on foreign agents are kept secret, or masked, unless a senior official requests an unredacted version.

Between Mr Trump’s election in November 2016 and his inauguration the following January some of the most senior figures in the Obama administration requested the unmasking of the reports that contained details of Mr Flynn’s conversations with the Russian ambassador.

They included Mr Biden, then vice-president, Samantha Power, the ambassador to the UN, James Clapper, the director of national intelligence, and John Brennan, the director of the CIA. They would not have known Mr Flynn’s identity until receiving the unmasked intercepts.