Gavin Williamson has been appointed defence secretary by Theresa May following Sir Michael Fallon’s resignation over claims of inappropriate sexual behaviour.

Williamson, 41, has been promoted to the job from the position of Chief Whip.

The South Staffordshire MP, who famously keeps a pet Tarantula named Cronus in his office, had not been seen as a frontrunner to replace Sir Michael.

Skipton and Ripon MP Julian Smith, 46, who was Williamson’s deputy in the Whip’s office, has been promoted to Chief Whip.

Smith now has the crucial job at the heart of government enforcing party discipline and attempting to make sure Tory MPs do as May demands.

Esther McVey, 50, the MP for Tatton and a former employment minister, has been made Deputy Chief Whip.

The reshuffle came as Westminster has been rocked by sexual harassment allegations against MPs and ministers.

Sir Michael resigned from the Cabinet on Wednesday evening following allegations he had behaved inappropriately.

He said he had “fallen below the high standards required”. The shock announcement came after it emerged he had repeatedly put his hand on a journalist’s knee at a dinner in 2002.

Cabinet Secretary Sir Jeremy Heywood is looking into claims made against May’s de facto deputy prime minister Damian Green and international trade minister Mark Garnier.

Ruth Davidson, the Scottish Tory leader, said this morning it was time for some “house clearing” in parliament using some “pretty big shovels”.

“The dam has broken on this now, and these male-dominated professions, overwhelmingly male-dominated professions, where the boys’ own locker room culture has prevailed, and it’s all been a bit bit of a laugh, has got to stop,” she told BBC Radio 4′s Today programme.