Boris Johnson emerged victorious from the EU referendum last week when just over half of voters backed a Brexit, a result that prompted David Cameron’s resignation as Prime Minister.
As one of the most prominent Leave campaigners, Mr Johnson was widely expected to put himself forward as a potential succcesor. Instead, he shocked MPs and journalists when, in a brief statement, he declared the next person to lead the Tory party “cannot be me”.
Mr Johnson told a press conference on Thursday: "My role will be to give every possible support to the next Conservative administration to make sure that we properly fulfil the mandate of the people that was delivered at the referendum and to champion the agenda that I believe in, to stick up for the forgotten people of this country.”
McGregor reacted with fury at his decision not to run in a tweet shortly after the news broke, lambasting Mr Johnson for striving to achieve the Brexit result and then abandoning the situation created by it.
"You lead this ludicrous campaign to leave EU," the Trainspotting actor wrote, "win, and now f*** off to let someone else clear up your mess."
Mr Johnson announced his decision hours after the Justice Secretary Michael Gove unexpectedly threw his hat into the leadership ring instead of backing Mr Johnson.
His about-turn was compared to the betrayal of Julius Caeser by Mr Johnson's father Stanley Johnson, who said his son was “probably very surprised” by the move. “'Es tu Brute' is my comment on that,” he told BBC Radio 4's The World at One. “I don't think he is called Brutus, but you never know.”
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