It’s not been a great week for Mrs May.

First came Nicola Sturgeon’s Scottish bombshell – we want a referendum and we want it now (or at least pre Brexit), she declared on Monday.

Then on Wednesday Mrs May had to perform a humiliating budget U-turn when she was forced to withdraw a proposed increase in National Insurance payments for the self-employed.

And the following day the Electoral Commission announced that the Tories were being fined £70,000 for fiddling their expenses during the 2015 election. In addition news came through that up to 20 Tory MPs were being investigated by the police for individual election expense fiddles – leading to a worst case scenario of the PM facing a series of difficult by- elections if any of the MPs are convicted.

And to finish her week, yesterday, it appeared Mrs May’s plans to change the way schools were being funded – which was going to hit schools outside the big cities – was likely to be withdrawn. Of course none of this amounts to anything like a crisis because whatever hole the Tories might have dug themselves into, they can be confident that Labour’s in a deeper one. This was particularly noticeable on Wednesday when 20 minutes after the budget U-turn Labour leader Jeremy Corbyn was unable to lay a glove on Mrs May during Prime Minister’s Questions.

Nonetheless, the Budget climb-down is quite striking not just because it was one of the fastest Budget U-turns in history but for what might, or might not, have lain behind it.

Here was a Chancellor renowned for his caution – allegedly nicknamed “spreadsheet Phil” – working next door to a famously cautious PM who never does anything before thinking and consulting about it once, twice, many times.

And yet like two blindfolded drunks after a good night out, the pair staggered into a main road not seeing the car marked Broken Election Pledge heading straight for them.

It’s often thought that governments break election pledges will-nilly but in fact it’s relatively rare.

It is true that there are many times when governments fail to deliver what they have promised, sometimes because events have intervened and sometimes because they haven’t even tried but complete reversal of policies are rare and dangerous.

Ask the Liberal Democrats who have never recovered from breaking their pledge not to increase student fees or the first president Bush whose soundbite “Read My Lips: No New Taxes” turned round to bite him back when he did precisely the reverse.

So how did it happen that neither the Chancellor nor the Prime Minister, nor their political advisers or civil servants, spotted the banana skin that awaited them?

In the 20015 campaign, admittedly under a different leader, the Conservative manifesto contained a specific pledge that income tax, VAT or National Insurance contributions would not be increased during the lifetime of a Conservative Government. Then in the first Budget under Mrs May this pledge was directly broken – “foolish” in the words of the then Conservative leader David Cameron (remember him?)

What made it worse were the attempts to claim that the pledge had not been broken because it only referred to contributions made by those on PAYE, although that is not what the manifesto said. The anger of those Conservative MPs and ministers who were forced to go on TV and radio and attempt to help the Government wriggle out of this mess was understandable.

Less understandable is how this came about in the first place. Some have suggested that, with a deviousness that would have put Machiavelli to shame, advisers in Number 10 allowed this to go through in the hope that this would undermine Hammond – a “wet”, as Mrs Thatcher used to call her more faint-hearted colleagues – as he is seen as less enthusiastic about a “hard Brexit” than other ministers

So is Mrs May the new Mrs Thatcher or just a pale imitation?

Certainly whatever one thought of Mrs T’s polices, until her judgement started to desert her in the latter years, she displayed great political agility. “The lady’s not for turning” she famously said but that is precisely what she did, when political events required it, she turned and turned often.

On the plus side for Mrs May it could be argued that this week she showed that she could turn when necessary, but on the minus side it has to be asked why was the turn necessary in the first place?

Sooner or later we will find out.

Ivor Gaber is Professor of Journalism at the University of Sussex and a former political journalist based at Westminster