Britain's Foreign Secretary Liz Truss and US Secretary of State Antony Blinken attend a G7 Foreign and Development Ministers Session with Guest Countries and ASEAN Nations in Liverpool, north-west England on December 12, 2021. Photo: AFP

British Prime Minister Boris Johnson appointed the foreign minister to lead talks with Europe Sunday after the resignation of the Brexit minister sent shockwaves through the already troubled London administration.

Foreign Secretary Liz Truss will take on the EU negotiating brief - including the knotty issue of Northern Ireland's relationship with Brussels - with immediate effect, Downing Street said in a statement.

The forced shuffle came a day after David Frost, a trusted ally of the prime minister and former Brexit negotiator, brought forward his resignation in a letter to the prime minister late Saturday.

He acted after The Mail on Sunday newspaper reported that he had handed in his resignation a week ago, but had agreed to wait until January before leaving his post.

In his resignation letter, Frost told Johnson that he had "concerns about the current direction of travel" regarding coronavirus regulations and tax rises.

Johnson is already reeling from a rebellion by 100 of his MPs in a parliamentary vote over coronavirus measures and the stunning loss of a 23,000-majority seat in a by-election.

That was partly blamed on a slew of reports that his staff and aides had held parties last Christmas despite virus restrictions in place at the time.

Adding to the government's problems, the website of The Guardian newspaper on Sunday published a photo of what appeared to be Johnson attending a drinks party in the garden at Downing Street.

The newspaper said it took place in May 2020, when COVID-19 restrictions forbidding such gatherings were in force, and those present were not observing social distancing guidelines.

AFP