Former Conservative MP Matthew Parris has deepened the rift among top Tories by using his Times column to launch a scathing attack on the pro-Brexit mayor of London, Boris Johnson.

Parris, a former aide to Margaret Thatcher, denounced Johnson for alleged dishonesty, vacuity, sexual impropriety and veiled homophobia.

“Somebody has to call a halt to the gathering pretence that if only you’re sufficiently comical in politics you can laugh everything off,” he wrote.

“Incompetence is not funny. Policy vacuum is not funny. A careless disregard for the truth is not funny. Advising old mates planning to beat someone up is not funny. Abortions and gagging orders are not funny. Creeping ambition in a jester’s cap is not funny. Vacuity posing as merriment, cynicism posing as savviness, a wink and a smile covering for betrayal … these things are not funny.”

Parris went on to detail Johnson’s sexual adventures and broken promises, as well as his dismissal from the Times as a correspondent for allegedly making up quotes.

He described the mayor as a “lacklustre” politician, and claims that Johnson was unable to defend his recent claims about the European Union in front of the Treasury select committee.

Referring to that performance, he wrote: “Watch a portrait in miniature of Johnson the politician: underprepared, jolly, sly, dishonest and unapologetic but (and this is the worrying part) horrifyingly vulnerable.

Parris added: “But there’s a pattern to Boris’s life, and it isn’t the lust for office, or for applause, or for susceptible women, that mark out this pattern in red warning ink. It’s the casual dishonesty, the cruelty, the betrayal; and, beneath the betrayal, the emptiness of real ambition: the ambition to do anything useful with office once it is attained.”

The attack prompted some conservative commentators to come to Johnson’s defence. MailOnline columnist Piers Morgan called Parris’s attack “vicious, spiteful, nasty and incredibly personal”.

Meanwhile, Iain Martin, editor of rightwing news website CapX, published a riposte. He claimed that supporters of Tory leader David Cameron were “losing the plot” out of fear of a leadership challenge should the country vote to leave Europe.

Ben Wallace, parliamentary under secretary of state at the Northern Ireland office, was one of the few serving politicians to speak out against Parris, tweeting him to say: “Unusually you are wrong on so many levels.”

Matthew Parris' vicious, spiteful, nasty & incredibly personal attack on @BorisJohnson makes me feel warmer to Boris & colder to Parris. — Piers Morgan (@piersmorgan) March 26, 2016

@MatthewParris3 have read your column today. Unusually you are wrong on so many levels. — Ben Wallace (@BWallaceMP) March 26, 2016

However, many readers backed Parris’s thesis. Iain Dale, the Tory-leaning presenter of LBC Drive, called the column powerful, and said it would be quoted for years to come.

The writer Will Black quipped: “Hi @MayorofLondon do you think Matthew Parris should be beaten up for this?”

By 3pm on Saturday, the column had been trending for six hours among UK Twitter users, who variously described his writing as splenetic, excoriating, eviscerating and brutal.