Last week it was jokes, this week it is brickbats. A week can be a short time in politics for a Chancellor. It was always an insult to the intelligence of the British public to say a National Insurance rise for 2.5 million self-employed people was not a broken election pledge when the Conservatives’ manifesto clearly stated there would be no such rises in this parliament if they got elected in 2015.

Even to continue to suggest, as No 10 did, that despite the latest U-turn, the UK Government had not broken a pledge is insulting and nonsensical. The farthest Philip Hammond would go was to say the centre-piece proposal of his first Budget did not meet the "spirit" of the Tory manifesto pledge on tax.

It transpires Theresa May and her Chancellor made the decision to change tack at a breakfast meeting yesterday following conversations with colleagues. But it leaves them open to the charge of incompetence and being able to be pushed around at the first sign of trouble.

No doubt, it was when Conservative MPs returned to their constituencies at the weekend that they were met with a tide of complaints from self-employed plumbers, window-cleaners, and hairdressers. The penny dropped.

Of course, Governments that change their minds – and this one has already reversed Budget decisions on child tax credits and disabled welfare payments – can make a virtue out of their embarrassment by insisting they listen to public concerns and are strong and mature enough to change their minds when they see the error of their ways.

Yet amid all the politicking there is a serious issue here; which is: how, given the greater flexibility in working practices, does the tax system deal with the increasing number of people who are self-employed and taxed less than others but do not enjoy the benefits employees have?

Some 15 per cent of the UK’s labour market is now self-employed, almost five million people, and there has been a rise in the number of people doing so-called "gig" work; the number of those on zero hours’ contracts is shooting up and now stands at more than 900,000.

The Government needs to consider seriously the Taylor Report that is looking at modern working practices and come back this autumn with some properly thought-through proposals that address the intricacies of today’s workplace.

The Chancellor will have to fill in the £2 billion black hole caused by the NI U-turn in his Autumn Budget. Mr Hammond can ill afford to make another blunder otherwise he will find himself on a short-term contract.