Boris Johnson is targeted by 'dirty tricks' campaign

Boris Johnson has been targeted by a 'dirty tricks' campaign, with his political enemies spreading unsubstantiated rumours about his private life after his bust-up with girlfriend Carrie Symonds.

With Mr Johnson commanding a seemingly impregnable lead among Tory members – despite sinking in polls of the wider electorate – rivals have spent the past week making increasingly wild claims about the conduct of his personal affairs.

One senior Westminster figure claimed to The Mail on Sunday last week that on the recording of the couple's heated argument which neighbours passed to the Guardian newspaper, Ms Symonds could be heard making allegations about a romantic friendship between Mr Johnson and a member of Commons staff.

The senior figure – who is not part of Jeremy Hunt's leadership campaign – said Ms Symonds had threatened the newspaper with an injunction to stop that claim from emerging.

But a source with close knowledge of the argument dismissed the smear, saying: 'Everything on that recording has been reported.' And a supporter of Mr Johnson said the Commons affair claim was 'completely bogus'.

The claim was just one of a welter of allegations – many of a sexual nature – which have been swirling around Westminster in the days since police were called to the South London flat which Mr Johnson shares with Ms Symonds.

His private life was raised at a leadership hustings in Carlisle yesterday, when he was asked by a Tory member: 'With a chequered private life, can we trust you with the great lady Britannia?' Mr Johnson replied: 'Every time I was asked to deliver something in London, I over delivered on my promises.'

He was also teased over reports that his row with Ms Symonds erupted after he spilt red wine on her sofa, with one Tory member warning him to lay off the wine. The leadership favourite replied: 'It is important not to spill a drop.'

But while the chaotic start to Mr Johnson's campaign has damaged his poll ratings among the electorate, it has barely dented his support among the Tory faithful.

With six days until ballot papers start landing on the doormats of the party's 160,000 members, a YouGov poll yesterday confirmed the findings of last weekend's Mail on Sunday survey by putting Mr Hunt (41 per cent) ahead of Mr Johnson (29 per cent) as the public's preferred choice to be the next Prime Minister. But Mr Johnson retains the support of two thirds of party members.

The widening gulf between his backing in the party and in the country as a whole has led to concerns that Mr Johnson's expected victory – handed to him by a tiny proportion of the electorate – will lack 'legitimacy' and dent party hopes that he will prove to be a natural Election winner.

MPs have also been alarmed by signs that the team of advisers around Mr Johnson, many of whom will follow him into Downing Street, has been fractured by feuding. They worry that aides and friends who have gathered around Ms Symonds, 31, have effectively set up an independent operation outside of Mr Johnson's formal team.

Yesterday, Mr Johnson took aim at Theresa May's leadership style.