He was replaced by Liz Truss whose term was so disastrous it was aborted after six weeks. She was replaced by Rishi Sunak who Johnson believes was a disloyal Chancellor of the Exchequer in his government.

Johnson, a former columnist and journalist, is already the author of several books including a biography of his favourite British prime minister, Winston Churchill, and an account of how London became the city we know today.

He had been working on a biography of William Shakespeare, but that has been shelved indefinitely.

His memoir will set off new speculation that his political ambitions are only temporarily dormant and that he may try to oust Sunak in a bid to regain Number 10 Downing Street.

Johnson remains in parliament and has not signalled any intention to quit his seat of Uxbridge and South Ruislip, despite all polls forecasting a Labour win at the next election in about 18 months.

Johnson has declared 63 financial interests from 24 different sources worth around £2.6 million ($4.6 million) on his MP register since the end of 2019.

He earned £27,000 from publishing house Hodder and Stoughton UK and £5990 from Harper Collins UK in the period.

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His total earnings are short of the £2.8 million declared by another former prime minister, Theresa May, who declared the highest values of extra earnings of all MPs in the House of Commons.

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