A DATE for your John Lewis diary: Wednesday, May 26.

This is when Dominic McKenzie Cummings becomes the main attraction at Westminster with an appearance before MPs inquiring into the UK Government’s (mis)handling of the Covid pandemic.

The former chief aide and blue skies thinker to Boris Johnson always carried a political health warning. David Cameron once, affectionately, branded him a “career psychopath”. Mr Cummings has also been variously likened to Machiavelli, Robespierre and Rasputin. And that was by his admirers.

Foolishly perhaps, the PM felt the need to ring up newspaper editors and accuse Dom of being the “chatty rat”, who leaked details of England’s second lockdown; a claim denied.

Indeed, Mr Cummings blogged that his former boss had fallen “below the standards of competence and integrity the country deserves”.

Speculation is rife the Pandora’s Box Dom carried out of Downing Street in his departure last November contained an array of compromising emails and taped conversations. The political storm swirling around our shaggy-haired premier seems to be deepening as time zips by, fuelled enthusiastically by his Labour and SNP opponents, who have votes in their eyes.

Its two main sources are: Boris allegedly raged about letting the Covid corpses “pile high in their thousands” rather than order another “mad” lockdown and who, initially, paid to sweep away Theresa May’s ghastly “John Lewis furniture nightmare” from the Downing Street flat and replace it with £58,000-worth of far more suitable top-end curtains, pillows and wallpaper.

Despite the PM’s forceful denials about those Covid remarks, his political opponents believe he uttered them. Indeed, Westminster’s chief Nationalist Ian Blackford openly branded Mr Johnson a liar in the Commons. The Speaker said the remark was “in order but not savoury”.

Yet until someone publicly confirms they heard Boris’s supposed outburst or it is proved he lied to Parliament, then the merry-go-round of claim and counter-claim will continue. Perhaps more of an immediate threat to Mr Johnson is the “cash for curtains” saga as it feeds the cronyism row.

Tory benefactor Lord Brownlow seemingly offered to pay £58,000 for the flat upgrade, only somewhere along the line the PM got jittery – Mr Cummings branded the process “unethical, foolish, possibly illegal” –and decided to dip into his pockets to pay for the swish furnishings from high society designer Lulu Lytle.

As expected, PMQs was a particularly acrimonious affair, turning into a contest between Captain Hindsight and the newly-dubbed Major Sleaze over who could sound more outraged.

Mr Johnson, who insists he has abided by the rules, clearly wouldn’t answer the question over the “initial” funding of his Downing Street flat, which suggests the Brownlow version is correct. The PM’s obfuscation will only lead critics to reinforce their view he is a “vacuum of integrity” and a “serial liar”; his “Kevin Keegan moment” at the end of his Commons clash with Keir Starmer suggested he was protesting too much.

Indeed, the political temperature has been building all week with ever more grandiose metaphors. The SNP’s Kirsten Oswald, who hit out at “Tory money- laundering” and Conservative oligarchs, went, dare I suggest, slightly overboard with her likening Boris to Louis XVI. While Downing Street is nice, Versailles it ain’t.

At the heart of the “cash for curtains” saga is the issue of how getting a Tory donor to pay for the refurbishment could be a conflict of interest and breach the ministerial code. But as we saw with Priti Patel, Mr Johnson is the “ultimate arbiter” over who has or has not broken the rules.

So, the appointment of Lord Geidt, HMQ’s ex-private secretary, as his adviser on ministerial interests, looks designed to give the appearance of independence when, in reality, there is none. And yet the crossbench peer’s first act could be to publish the long overdue list of ministers’ interests, which could throw some light over flatgate. I suspect, however, it won’t materialise before polling day.

Also, failing to declare a donation from a donor would be a breach of Electoral Commission rules but these can be dodged by claiming the money was a loan rather than a gift. Yet, in theory, now the political spending watchdog has launched its own probe into the affair, it could lead to those nice people from Scotland Yard having a word in Boris’s ear.

So, there are now three probes into flatgate; all of which would be rendered unnecessary if the PM simply answered the pertinent questions; his refusal to do so reinforces the suspicion he is desperately playing for time and that an even bigger political iceberg is lurking in the Westminster darkness.

Whether or not any of this soap opera is cutting through to the public consciousness will probably only be known in the 48 hours after the polls close next week. Tory hearts will be pounding.

The UK Government’s contention is the claims of sleaze and cronyism are just “vexatious” tittle-tattle; that, amid the pandemic, the public doesn’t care about the disgruntlements of a former adviser or opposition leaders but want ministers to focus on the main task of recovery. Yet, integrity matters; judgment matters. Voters do not take kindly to clever dick politicians who seek to pull the wool over their eyes. There is always a price to be paid for such foolishness.

As time passes, it may just be the sheer weight of controversy reaches a tipping point not only for voters but for the Tory party too. Those men, and women, in grey masks may be planning a post-May 6 socially-distanced meeting to consider their options.

In terms of his capacity for being a market leader in generating negative headlines, Boris, while he might dislike its furniture, is loyally adhering to the famous John Lewis slogan: never knowingly undersold.