For five days, the UK government staunchly defended the controversial algorithm that determined A-level grades before ditching the model because of “significant inconsistencies”.

On Monday, ministers announced they will allow for results to be based on teachers’ predicted grades for their students, rather than a “standardisation model” that saw the A-level grades of almost 40% of students downgraded from what they had originally been awarded.

It followed criticism from students and headteachers and complaints from dozens of Tory MPs, and came more than a week after the Scottish government was forced into its own U-turn after a backlash about the moderation system used there.

Yet despite the advance notice of the chaos, UK government ministers repeatedly insisted they would not follow the example set in Holyrood, arguing an appeals system would resolve most problems.

The government in England on the eve of the results outlined a “triple lock” process: this would allow a pupil to either accept their calculated grade, appeal to receive a valid mock result, or sit a new exam in the autumn.

And ministers didn’t appear likely to budge after prime minister Boris Johnson summed up the government line when defending the “robust” system. On Thursday, he told reporters that the results were “good” and are “dependable for employers”.

Speaking on Sky News on the same day, Williamson was clear there would be no volte face.

He was asked by Niall Paterson: “Can you give a cast-iron guarantee, triple-locked if you will, that you will not be forced into an embarrassing U-turn?”

“Absolutely,” replied Williamson.

That day, the president of the National Union of Students launched a petition against the policy and accused the government’s system of being “racist and classist”.

Larissa Kennedy made the comments on Twitter, writing: “Congrats to those getting results today.

“Due to a classist, racist moderation system, not everyone will receive the grades they deserve.”

The petition claimed the Department for Education’s “triple lock” system amounted to “educational inequality” and was based on a “ridiculous algorithm” which unfairly prejudices students from less advantaged backgrounds.

Dr Michelle Meadows, executive director for strategy, risk and research at Ofqual, responded that there is “no evidence of systematic bias” in the moderation system.

Still little sign of a U-turn.

On Friday, scrutiny of the impact of the moderation heightened.

With neither the Department of Education or education watchdog Ofqual yet to signal any alteration in the policy, Williamson’s Whitehall department were moved to post a blog that claimed it had “debunked” misleading claims in the media.  

The blog, largely an exercise in semantics, was readily re-tweeted by senior Tories, including by former education secretary Michael Gove. It repeatedly makes a defence of the now ditched “standardisation model” and even suggests it is superior to the “entirely different” approach taken in Scotland.

On Saturday, students marched on Westminster and called for the education secretary to be fired. Placard-waving demonstrators chanted “Sack Gavin Williamson!” and “Teachers not Tories!”.

On the same day, Williamson gave an interview in The Times where he defended the model once more – and knocked the system deployed north of the border.

“No U-turn, no change,” he told the paper’s Steven Swinford, adding that “there aren’t any controls, you’ve got rampant grade inflation” in Scotland.

The message was clear: England had done it better than Scotland, and there would be no junking of the algorithm.

Fast forward two days and suddenly there is a very different tone, with the morning briefing to journalists in the Westminster lobby hinting at an imminent big announcement. 

By the afternoon, Ofqual’s chairman Roger Taylor, fronting that announcement, admitted the regulator had gone down the “wrong road”. And Williamson said he now accepted the model had produced more “significant inconsistencies” than could be rectified through an appeals process. 

Remarkably, the minister claimed the scale of the problem had only become clear over the weekend. “As we looked in greater detail over Saturday and Sunday, it became evident that further action needed to be taken,” he said, which commentators took as an attempt to blame the regulator for the fiasco.