Team Boris HQ: Westminster mansion where Michael Portillo plotted to topple John Major 24 years ago

Boris Johnson is plotting his takeover of No 10 in a Westminster townhouse with a history of disloyal scheming.

The leadership frontrunner has set up his campaign headquarters at 11 Lord North Street – where Michael Portillo ran his doomed coup against John Major 24 years ago. The then Defence Secretary’s machinations were revealed when BT engineers were spotted installing 40 phone lines, despite his public declarations of loyalty to the Prime Minister.

Now the £3.6 million home of Tory peer and donor Greville Howard is the nerve centre of what insiders have dubbed Mr Johnson’s ‘government in exile’ – where he is planning a wholesale clearout of party and Government figures if, as expected, he gets into Downing Street.

Behind the Georgian facade on one of the country’s most expensive streets, the ornate dining room has been turned into a ‘comms centre’ while the grand sitting room serves as a ‘war room’. Aides cluster on a large L-shaped sofa with TVs showing all the news channels, and maps of constituencies are draped over the aristocrat’s expensive art collection.

Donors are urging Mr Johnson to begin preparations for an Election, and approach ‘a select number of serving permanent secretaries’ – as they hope one of his first acts in No 10 will be to oust controversial Cabinet Secretary Sir Mark Sedwill.

One millionaire backer of Mr Johnson told The Mail on Sunday: ‘He’s going to need a comprehensive clearout, a new chairman and a new treasurer of the party.

And that’s before he even starts on Whitehall.’

Australian election guru Sir Lynton Crosby and Mr Johnson’s girlfriend Carrie Symonds are ‘feeding into the campaign in an unofficial capacity’. The activity is being formally headed by former London mayoral candidate Zac Goldsmith and former Defence Secretary Gavin Williamson, both tipped for top jobs in Mr Johnson’s government.

Day-to-day running of the campaign is overseen by coordinator James Wharton, a Tory MP between 2015 and 2017 and a close ally of Mr Williamson.

Former Tory Party chairman Grant Shapps runs a vast spreadsheet of exactly who every Conservative MP is backing – boasting that he had correctly predicted Mr Johnson’s barnstorming 114 votes in the first round.

Behind the Georgian facade on one of the country’s most expensive streets, the ornate dining room has been turned into a ‘comms centre’

Liz Truss is heading up policy, with the Treasury No 2 heavily tipped to step up to Chancellor in a Johnson Government – a role also coveted by leadership rivals Sajid Javid and Matt Hancock, who dropped out of the race on Friday. Long-time Johnson ally Ben Wallace, the Security Minister, is widely expected to get a Cabinet job, too.

Mr Johnson’s team insist no jobs have been promised, but a potential return of Mr Williamson weeks after he was sacked for allegedly leaking details of a National Security Council meeting about Chinese telecoms giant Huawei could prove problematic, as it would put them in conflict with Sir Mark Sedwill, who was instrumental in his firing. Asked last week if he could work with Mr Williamson again, Sir Mark refused to comment, saying only: ‘You must think I was born yesterday.’

Mr Johnson also needs to recruit a powerful Chief of Staff, with former City Hall officials Sir Edward Lister and Will Walden tipped to return to his side. Mr Walden will spend the next three days preparing Mr Johnson’s for Tuesday’s BBC debate.

Meanwhile, insiders say Mr Johnson’s father Stanley has been tasked with keeping Boris’s Remainer siblings Jo and Rachel on a tight leash.