BORIS Johnson has been accused of “sacrificing” his brother after Jo Johnson, the UK Universities Minister, dramatically quit this morning, saying he had been "torn between family loyalty and the national interest".

The bombshell decision by Mr Johnson, who is not only leaving Government but also quitting politics altogether, adds to the fractious atmosphere gripping Westminster and the tussle over Brexit between the Conservative Government and the UK Parliament.

It will also throw up more question-marks about the Prime Minister’s approach to government, which his critics have denounced as “Trumpian”.

His brother’s shock announcement also came just hours before the Conservative leader was due to give a keynote speech in Yorkshire, marking what Downing St regards as the first day of the election campaign.

READ MORE: Nicola Sturgeon quizzed on Brexit, sectarian marches and Scotrail in heated FMQs

In his announcement on social media, Mr Johnson, who was elected MP for Orpington in May 2010, said there had been an "unresolvable tension". In his role, he had been able to attend Cabinet meetings alongside his older brother.

He tweeted: “It's been an honour to represent Orpington for 9 years & to serve as a minister under three PMs. In recent weeks I've been torn between family loyalty and the national interest - it's an unresolvable tension & time for others to take on my roles as MP & Minister. #overandout."

Mr Johnson is pro-European and has previously called for a second referendum, a position that puts him at odds with the PM, who has vowed to leave the EU on October 31 with or without a Brexit deal.

Nick Boles, the former Conservative minister, who resigned from the party to sit as an independent, said: “Johnson is willing to sacrifice anyone and anything on the altar of his ego and ambition. His lust for power consumes everyone who stands in his way.”

Labour’s Angela Rayner noted: "Boris Johnson poses such a threat that even his own brother doesn’t trust him."

Naomi Smith, Chief Executive of the pro-EU Best for Britain campaign said: "Boris Johnson has already managed to lose his parliamentary majority, his first three votes, his first by-election and now his own brother.

"This is the evidence that Johnson and Cummings have no great plan, only a misguided, blind belief in their own alleged abilities. It is time for this madness to stop," she added.

READ MORE: Alison Rowat: A premiership remarkable for all the wrong reasons

Fellow Independent Sam Gyimah, who had the Tory whip removed this week, tweeted: "Honest Jo Johnson is a top talent & will be a big loss to politics. It was an immense privilege to (follow on from) him as Universities & Science Minister.

"Huge admiration for him in resolving an impossible and painful 'conflict of loyalty' in the national interest," added the Surrey MP.

A No 10 spokesman: “The PM would like to thank Jo Johnson for his service. He has been a brilliant, talented minister & a fantastic MP. The PM, as both a politician & brother, understands this will not have been an easy matter for Jo.”

In 2013, in the wake of Ed Miliband successfully challenging his brother David for the Labour leadership, Boris Johnson said: "We don't do things that way, that's a very left-wing thing. Only a socialist could regard familial ties as being so trivial as to shaft his brother."

He added: “Only lefties can think like that...They see people as discrete agents devoid of ties to society or to each other, and that's how Stalin could murder 20 million people."

One Tory MP quipped: “Jo Johnson has resigned to spend less time with his family.”