A “substantial minority” of Labour MPs would not support Jeremy Corbyn being Prime Minister, Chuka Umunna has claimed.
Mr Umunna, a former Labour and Change UK MP and now a Liberal Democrat, said he had spoken to a number of Labour MPs would “simply would not countenance” the party’s leader becoming PM.
He told BBC Radio 4’s Today programme: “The problem there is with the prospect of Jeremy Corbyn taking up the role of leading an emergency government is he cannot command a majority among his own MPs, never mind others like Conservative rebels who would refuse to give him confidence.
“I know, because I have spoken to them, there is a substantial minority of Labour MPs at the very least who simply would not countenance Jeremy Corbyn being the prime minister of this country.
“So the question is, is there a figure who, as an alternative, could command a majority?”
Mr Umunna’s comments come as Jeremy Corbyn has called on Cabinet Secretary Sir Mark Sedwill to rule that Boris Johnson cannot go ahead with a no-deal Brexit if there is a general election.
He said it would be an "unprecedented, unconstitutional and anti-democratic abuse of power".
According to reports Mr Johnson could try to hang on to make sure Britain leaves the EU before going to the polls if he is defeated in a vote of confidence when MPs return in September.
If he is defeated in a no-confidence motion he would have 14 days, under the Fixed Term Parliaments Act, to win another vote of confidence or, if no other government could be formed, face a general election.
In his letter to Sir Mark, Mr Corbyn wrote: "Forcing through no-deal against a decision of Parliament, and denying the choice to the voters in a general election already under way, would be an unprecedented, unconstitutional and anti-democratic abuse of power by a Prime Minister elected not by the public but by a small number of unrepresentative Conservative Party members.
"A Labour government will never support a no-deal exit, so would of course want the opportunity to take a different view."
Officials said Sir Mark would be reply to Mr Corbyn, but senior Conservatives dismissed the letter as a "political stunt".
A senior Conservative source said: "Jeremy Corbyn will do anything to get his hand on the keys to number 10.
"No amount of letter-writing political stunts will change the fact that politicians don't get to choose which public votes they respect."