The race to succeed Boris Johnson as British Prime Minister got bloody for the governing Conservative Party on Sunday, with reports of damaging briefings against frontrunner Rishi Sunak and even a so-called mucky memo or dirty dossier doing the Tory WhatsApp group rounds.

The 424-word attack seen by The Sunday Telegraph' contains personal attacks branding the British Indian former Chancellor a schoolboy and a liar , who cannot be trusted on tax.

Headlined Get Ready for Rishi , after Sunak's Ready4Rishi campaign launch, the memo reportedly brands the 42-year-old MP as having a Big Tax and Big Spend agenda.

It's coming from that Thatcherite wing of the party that was loyal to Boris, the newspaper quoted a source as saying.

There's a lot of runners and riders and a frontrunner at the moment trying to create a coronation scenario. The dossier would suggest that he's actually got a pretty poor record that's not opinion, it's fact. This is about winning the next general election. That's why it's being circulated. It's spread like wildfire. There won't be a Tory MP who hasn't seen it by now, the source said.

The memo criticises Sunak personally, saying he publicly lied when seeking to explain his Indian wife Akshata Murty's legal non-domicile tax status.

Pointing to the fact he secretly" held a Green Card to work in the US 18 months into his chancellorship of the UK, it casts doubt over his claim that his resignation within minutes of [fellow Cabinet minister Sajid Javid] was an unplanned coincidence , pointing out that he launched his campaign for the leadership of the Conservative Party with a website domain registered in December last year.

The memo also attempts to tarnish the former Chancellor with Johnson's dubious partygate legacy of COVID law-breaking parties in Downing Street, saying: Like Boris, (he) landed a 'partygate' fine from the police for breaking lockdown rules .

Tax, over which Sunak and former boss Johnson are known to have clashed, will become a central focus of the leadership campaign for a staunchly low-tax Conservative Party.

Sunak has been candid in declaring that tax can be cut only when finances and the global economic situation improve and urged in his campaign launch video to not be swayed by fairy tale promises.

"Do we confront this moment with honesty, seriousness and determination or do we tell ourselves comforting fairy tales that might make us feel better in the moment but will leave our children worse off tomorrow," he questioned.

Many in Johnson's camp see his unceremonious departure from 10 Downing Street as being precipitated by Sunak's resignation and are therefore determined to block his campaign.

Clearly the Prime Minister remains deeply bruised by the Chancellor's resignation. Rishi's camp will have to soak up a lot of anger over the days to come. That will apply to whoever takes over, Sir Charles Walker, a former vice-chairman of the 1922 committee of Tory backbenchers, told the 'Observer' newspaper.

Senior Tories are pleading for restraint as the war of words threatens to tear the governing party apart and damage its chances in the next general election, expected by 2024.

Lord Michael Howard, who led the party between 2003 and 2005, told The Sunday Times': I am dismayed by some of the attacks being made on Rishi Sunak. It is essential for the sake of the party and the country that this leadership contest is conducted in a respectful manner.

The party and the country need some calm reflection and the chance for candidates to put forward their positive plans. Conservatives should be careful not to spend their time undermining some of their own leading figures, added Lord William Hague, another former leader.

The newspaper also claims that dossiers on extramarital affairs and other allegations of dubious conduct are being put together within Tory party ranks on almost all contenders in the race, now adding up to nearly 10.

It comes as fresh allegations emerged that Johnson had lobbied for a job for a young woman who claims she was having a sexual relationship with him during his time as London Mayor.

According to The Sunday Times', the appointment was blocked because Kit Malthouse, then a senior figure in City Hall and now a Cabinet minister, suggested the pair had an inappropriately close relationship. Johnson is said to have admitted pushing her forward for a job when the woman, who remains anonymous, confronted him in 2017.