Former British prime minister Boris Johnson has already earned more than £1 million ($1.2 million) for giving paid speeches since leaving office in September, according to an official register of UK parliamentarians' interests.

Famous for his rhetorical flourishes, Johnson has in recent months delivered speeches to bankers in New York, insurers in the United States, a summit organised by broadcaster CNN in Portugal and another talk in India.

He received payments ranging from £215,000 to £277,000 ($267,000 to $344,000) each time, according to the official document published on the UK parliament's website that lists lawmakers' financial interests.

Johnson, 58, left Downing Street after announcing his resignation in July following a series of scandals that tarnished his premiership, but still serves as an MP for the ruling Conservative party.

He attempted to make a spectacular political comeback after the rapid demise of his successor Liz Truss triggered another Conservative leadership contest, but Tory MPs backed his former finance minister Rishi Sunak instead.

Johnson, who remains popular with Tory members, has not ruled out another bid for the top job, saying he was "well placed to deliver a Conservative victory in 2024" as the main opposition Labour party rides high in the polls.