The UK’s Brexit Minister Lord Frost has resigned “with immediate effect”, adding to the strain on Boris Johnson after a tough few days for the British prime minister.

Johnson is battling a huge rise in COVID-19 infections, a party rebellion over tightened lockdown restrictions, an unexpected by-election defeat and ongoing controversy over lockdown-breaking festive celebrations.

Lord Frost, who has led negotiations with the EU, quit his post on Saturday, telling Johnson that building a new relationship with the European Union would be a “long-term task”.

He is believed to have handed in his resignation letter to Boris Johnson last week with an agreement to leave in January.

But in a letter to the PM released on Saturday evening, he said he was “disappointed that this plan has become public this evening and in the circumstances I think it is right for me to write to step down with immediate effect.”

Lord Frost thanked Johnson and said “Brexit is now secure”.

“The challenge for the Government now is to deliver on the opportunities it gives us,” he said in the letter.

“You know my concerns about the current direction of travel.”

Frost also said he was sad the unlocking from COVID-19 restrictions in the UK had not proved “irreversible” as promised, and added, “I hope we can get back on track soon and not be tempted by the kind of coercive measures we have seen elsewhere”.

Lord Frost’s resignation is the latest in a series of recent setbacks for Johnson.

• Scientific advisers have warned that, despite the ramping up of the booster program, the rapidly-spreading Omicron variant still presents a threat which could see at least 3000 hospital admissions a day in England.
• The advice was published just days after the PM suffered the worst rebellion of his leadership, when some 100 Tories voted against a tightening of the rules in the form of mandatory COVID health passes for large venues.
• The loss of what had been the ultra-safe Conservative seat of North Shropshire – in a by-election triggered by a Tory sleaze scandal – to the Liberal Democrats.
• A Christmas party controversy has rumbled on, as Cabinet Secretary Simon Case, the man in charge of investigating lockdown-breaking festive gatherings reported to have been held in Downing Street and the Department for Education last year, “recused himself” following allegations of such events in his own department.
• Ministerial interests adviser Lord Geidt “asking questions” about lavish refurbishments at 11 Downing Street over allegations the Prime Minister may have misled him.
• In November, Johnson insisted he thought a major speech to business leaders in which he lost his place in his notes, talked about a day trip to a Peppa Pig theme park and imitated a car, “went over well”.

-AAP