A parliamentary select committee has questioned Michael Prescott, the adviser who wrote the memo that led to the resignation of the BBC’s director general, Tim Davie

Senior figures running and advising the BBC have been questioned about the crisis at the broadcaster, which has been threatened with a $1bn lawsuit from Donald Trump.

The BBC’s director general, Tim Davie, and the head of news, Deborah Turness, resigned this month after controversy triggered by the leak of a memo written by a former external adviser.

Their departures followed a disagreement over how to respond to the memo from Michael Prescott, which claimed there were “serious and systemic problems” at the corporation and alleged liberal bias in its coverage of the US election, Gaza and racial diversity and transgender issues.

Coverage of the memo and its consequences have triggered internal talk of a rightwing “coup”, board splits and crippling delays.