The Times has learnt that the Conservative MP for Henley has agreed to announce his resignation on December 8 after six sometimes turbulent years at the helm of the house journal of the Tory party.

The departure is timed to coincide with the result of his Party’s leadership contest the previous day. If David Cameron wins, he is expected to offer Mr Johnson, a fellow Old Etonian, a frontbench job.

Andrew Neil, the chief executive of The Spectator, wants the next Editor to be full-time and uncompromised editorially by putting loyalty to the Party leader before the magazine.

Mr Johnson, 41, has been on the back benches for a year after being sacked by Michael Howard for lying about his affair with Petronella Wyatt, a columnist on the magazine. The affair with Ms Wyatt, 37, was just one element in a drama that turned the magazine, the oldest in the English-speaking world, into a laughing stock.

Kimberly Quinn, its married publisher, was exposed as having had an affair with David Blunkett, who was then the Home Secretary.Rod Liddle, an associate editor of the magazine, was also revealed to have left his wife and children for a secretary at the magazine.

The series of extramarital trysts formed the basis of a satire on the magazine, Who’s the Daddy?, which played to packed houses over the summer at the King’s Head Theatre in Islington, North London.

For Sir Frederick and Sir David Barclay, who took over the magazine when they bought the Telegraph group of newspapers in July last year, the stage show, in which the magazine was nicknamed The Sextator, was the final straw.

Sales and profitability have risen under Mr Johnson, but the proprietors thought that the intellectual content had deteriorated.

Three names are being mentioned as his successor: Peter Oborne, the magazine’s Cambridge-educated political editor; Matthew d’Ancona, 37, the deputy editor of The Sunday Telegraph and a Fellow of All Souls College, Oxford; and Quentin Letts, 42, the parliamentary sketchwriter for the Daily Mail.

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