British Prime Minister Boris Johnson on Wednesday appointed a new-look cabinet to revamp his Brexiteer government after controversies over Covid, Afghanistan and taxes, demoting his under-fire foreign secretary.

Dominic Raab was moved to the lesser role of justice secretary but will retain the title of deputy prime minister, Downing Street confirmed.

The former lawyer, who deputised for Johnson when he was in intensive care with Covid-19 in April last year, has faced sustained criticism for his handling of the Afghan crisis.

He was replaced by International Trade Secretary Liz Truss, who has brokered a series of deals since Britain's full exit from the European Union in January. 

She is only the second female foreign secretary in British history and one of six women in Johnson's 23-strong team, up from five before but still down on his recent predecessors' cabinets.

"The cabinet I have appointed today will work tirelessly to unite and level up the whole country," the prime minister tweeted.

"We will build back better from the pandemic and deliver on your priorities. Now let's get on with the job."

Among the other leading offices of state, finance minister Rishi Sunak -- who has overseen big-spending economic support during the pandemic -- and hardline interior minister Priti Patel both retained their roles.

Gaffe-prone Education Secretary Gavin Williamson meanwhile was sacked. He tweeted that it had been a "privilege" to serve in his role since 2019 when Johnson took office on a vow to "get Brexit done".

Now that Britain has formally left the EU after a years-long divorce process, the Conservative government has been battling to tame one of the world's highest per-capita death tolls from the pandemic.

Johnson enjoyed a "vaccine bounce" after Britain led the Western world in a mass immunisation programme, but the Conservatives' lead over the main opposition Labour party has eroded in recent opinion polls.

Last week, Johnson broke an election promise not to raise taxes as he announced a new levy to fund the beleaguered state-run National Health Service (NHS) and elderly care.

Angering some Conservative right-wingers, Johnson this week outlined a plan to restore pandemic restrictions if needed, to avert a fresh crisis for the NHS heading into what could be a difficult winter.

- 'Absolute idiocy' -

He also faces criticism for failing to flesh out his "levelling up" agenda to rebalance growth in deprived regions of Britain, including former Labour strongholds of northern England.

Brexit point man Michael Gove took on cabinet responsibility for levelling up, as he replaced Robert Jenrick at the ministry of housing, communities and local government.

Raab was on holiday on a Greek island as the government scrambled to evacuate British nationals and Afghan staff in the face of Taliban advances last month.

The opposition Liberal Democrats said Johnson should have fired him.

"Raab is the latest member of this Tory government to be rewarded for failure. After his catastrophic handling of the Afghanistan crisis, he should be out of government altogether," the party said.

Truss's successor as trade secretary was named as Anne-Marie Trevelyan, whose old department for international development was subsumed into the foreign office last year.

Williamson meanwhile has faced a barrage of complaints about his handling of school closures, examination arrangements and university admissions during the coronavirus emergency.

Labour's deputy leader Angela Rayner said Williamson, who last week muddled up two of Britain's most prominent black sportsmen, "should have been sacked over a year ago".

His "absolute idiocy, failures and uselessness have damaged life chances of our country's children and this government has failed young people, teachers & education staff" she tweeted.

Asked about the number of women in the top team, Johnson's official spokesman said the premier understood "the importance of having a diverse cabinet". 

But Amanda Milling was ditched from her cabinet role as Conservative co-chairwoman, just two weeks before Johnson rallies party members at their annual conference.