Regulators across the world have been assessing changes made to the MAX and its anti-stall software, after the plane was grounded in March 2019 following two crashes which killed a total of 346 people.

Britain's Civil Aviation Authority (CAA) lifted the ban on the MAX, making its first significant aviation safety decision since formally leaving the European Union and the EU Aviation Safety Agency (EASA), on Dec. 31.

"This is not a decision we have taken lightly and we would not have allowed a return to service for UK operators, or lifted the ban on the aircraft operating in UK airspace, unless we were satisfied that the aircraft type is airworthy and can be operated safely," said CAA chief executive Richard Moriarty.

EASA said the MAX was safe to return to service earlier on Wednesday, with the CAA following suite. The United States lifted its ban in November, followed by Brazil and Canada.

Most of the work done on the MAX was completed last year while Britain was still part of EASA and the CAA said it worked alongside EASA on the process.

UK airlines will be able to operate passenger flights with the MAX subject to close oversight, said the CAA, including new pilot training, adding it was in close contact with travel group TUI, the only UK operator of the aircraft.

(This story removes extraneous letter in fifth paragraph.)

(Reporting by Sarah Young. Editing by Andrew MacAskill)