Day four of impeachment hearings saw the most explosive testimony so far as Gordon Sondland, the US ambassador to the European Union, claimed Donald Trump had directed a quid-pro-quo with Ukraine through his personal lawyer Rudi Giuliani.

Sondland asserted that an Oval Office meeting with Trump was conditional on Ukraine announcing investigations into Burisma, a gas company linked to the son of the former vice-president Joe Biden, and a widely discredited conspiracy theory that Ukraine planted evidence on a server of the Democratic party to show that Russia interfered in the 2016 election.

'We followed the president’s orders,' said the Trump appointee in remarks that sent shockwaves through Washington and elicited a furious response from the president.