Boris Johnson’s own brother quits government

British Prime Minister Boris Johnson was dealt a fresh blow on Thursday when his younger brother quit the government, citing the national interest.

Jo Johnson had campaigned strongly against Britain's exit from the European Union in 2016, a position that put him at odds with his older and more famous brother Boris.

But he took a job in his brother's government as universities and science minister, a position he had held previously.

"It's been an honour to represent Orpington (a London suburb) for nine years & to serve as a minister under three prime ministers," Jo Johnson tweeted.

“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,” he tweeted.

The resignation of Jo Johnson, who like his brother Boris is a former journalist, comes after 22 MPs left the governing Conservative party this week.

One MP defected to the pro-European Liberal Democrats and 21 were expelled for voting against the prime minister's Brexit strategy.

His resignation also comes the day after MPs voted to legislate to stop Boris Johnson taking Britain out of the European Union without a divorce deal on October 31.

The premier said his brother had been “a brilliant, talented minister and a fantastic MP”, and that the decision would not have been easy.