The story of why every infant in England is entitled to a free school meal has all the ingredients of a Westminster sitcom: high politics and low farce, “moaning” headteachers and an electoral thunderbolt that no one saw coming, all sprinkled with a light dusting of celebrity.

The way former deputy prime minister Nick Clegg tells it in his memoirs, it all started when Michael Gove “stumbled across” Henry Dimbleby, cookery writer and founder of the Leon restaurant chain, on a holiday in Marrakech.

Gove, then education secretary, commissioned Dimbleby and his business partner John Vincent to write a report about improving food in schools. The resulting School Food Plan was duly published in July 2013. It recommended that the government “should embark upon a phased roll-out of free school meals for all primary school children, beginning with the local authorities with the highest percentage of children already eligible for free school meals”.

The report cited the results of pilots of free school meals for primary children in Durham; Newham in East London; and Wolverhampton. It said that “eating well improves performance in all academic subjects, and a busy, popular dining hall brings intangible benefits to the culture of the school”.

The authors also hailed “the positive impact on children’s health, the unifying social effect of having the whole school eating together, or the many other pleasures that come from eating good food in company”.

This was, the report also noted, the only recommendation it had made that the government was not agreeing to implement immediately. But this was the era of coalition government, when policy was decided by backroom bartering between the Conservatives and Liberal Democrats; and that autumn both parties needed big announcements to sell to their respective party conferences.

The Tories were determined to make good their manifesto pledge to introduce a marriage tax allowance, with a £600 million price tag. It was a policy deemed “idiotic and wasteful” by Lib Dem schools minister David Laws, and the cost of his party’s acquiescence was a policy of their own, worth the same amount.

Eventually, they settled on free school meals, but just for infants - not all primary children, as recommended in the School Food Plan. And the policy would be introduced across the country in one go, instead of being targeted at poorer communities first. With a September 2014 start date, schools had less than a year to prepare. Universal infant free school meals, UIFSM, was born.

For Clegg, then leading the Lib Dems, the policy would teach younger children healthy eating habits, save hard-pressed families money and boost educational attainment. For critics like blogger Andy Jolley, it was a costly policy based on a dubious evidence base that left poor families paying for richer family’s lunches through their taxes.

To describe UIFSM as unpopular with Gove - who was Laws’ boss at the Department for Education - is to understate his opposition. The junior minister’s diary outlines 12 months of poisonous war within the department.

It describes how Gove and his adviser Dominic Cummings fought efforts to put the policy into law - something that would limit the autonomy of free schools and academies - and tried to “sabotage” the plan, feeding journalists damaging front-page stories portraying a policy in chaos.

Laws even records an occasion when Treasury officials were prevented from entering the DfE to discuss funding to help schools deliver the policy, and a row about the location of a Lib Dem adviser’s desk in the DfE that led to an exasperated prime ministerial phone call.

For his part, after leaving government, Cummings went public with an email claiming that “officials in the DfE were unanimous it was a bad gimmick and introduced in a way that makes it hard to avoid implementation chaos. Officials were obviously right.”

But while UIFSM excited the Westminster bubble, Laws’ diaries also acknowledge, albeit disparagingly, some of the concerns of schools which had to implement it.

On 25 March 2014, he appeared on BBC Radio Somerset. In his diary, he complains about “some whingeing headteacher moaning about how difficult it’s going to be to implement this policy”. “Why doesn’t she just get on with it - it’s hardly rocket science,” Laws concludes.

But for many schools, there were real challenges on numerous fronts, from having to build or extend kitchens and creating enough space for all the children to eat their lunches, to finding money from their own budgets to top up insufficient government funding.

One headteacher told researchers at the Education Policy Institute (EPI) that UIFSM “had huge implications; extra kitchen staff, transport between sites, extra lunch supervisors, split lunch time...Stock control and ordering are important, as storage is an issue.”

As well as the original £600 million, a further £180 million had to be found to help schools with building work and new equipment; small schools received an extra £3,000 each in recognition of the particular problems they faced.

Despite the huge sums involved, and the millions of young children affected, it is striking how little the effects of the policy have been studied, even now, almost four years after it came into effect.

EPI published a report in January - but avoided rigorous analysis of the educational impact. The Institute for Social and Economic Research began another study, which will include this, in the same month. But official government research? There is none.

EPI estimated that despite DfE funding, UIFSM initially cost schools an extra £125 million across 2013-14 and 2014-15, although it also says they received £38 million more funding for the free meals than their revenue costs in 2015-16.

“So far,” the authors say, “the funding of schools to deliver UIFSM appears to have been adequate on average, but a small proportion of schools have seen an increase in deficits in school meal provision.”

In their 2015 election manifesto, the Conservatives pledged to keep UIFSM, but once they were back in government without the Lib Dems, their doubts seemed to re-emerge.

That autumn, Downing Street had to quash speculation that the Treasury wanted to axe it to save money, and the following February it emerged that the grants for small schools were being dropped. The DfE said it had always told schools they were temporary.

Then, in 2017, UIFSM received what looked like the killer blow. With Theresa May seemingly cruising to a majority after calling a snap election, her party’s manifesto boldly stated what many Tories had long thought in private: “We do not believe that giving school lunches to all children free of charge for the first three years of primary school - regardless of the income of their parents - is a sensible use of public money.”

Free school meals for all infants would be scrapped - although free lunches for the poorest would remain - and the cheaper option of providing free breakfasts for all primary school children would be introduced instead. The proposal was branded a “disgrace” by celebrity chef Jamie Oliver, who has campaigned on healthy school meals since highlighting the dangers of Turkey Twizzlers in 2005.

By contrast, Labour promised to extend free school meals to all primary children, funded by placing VAT on private school fees.

In the event, the policy of universal free school meals for infants was saved as efforts to scrap it evaporated along with May’s majority in June’s unexpected election results.

Has UIFSM been worth it? EPI surveyed teachers and found that more than a third thought it had improved pupils’ attainment and concentration. Teachers’ unions are also positive.

But the government has not increased the £2.30 it gives schools for each meal they serve since 2014 and the EPI warns that inflation is likely to make current government funding “insufficient”.

The report’s authors warn that under this scenario, “the net costs to schools - and the existing impacts on wider curriculum delivery and school staff time - will be increased, potentially undermining wider benefits that might be realised”.

So a policy that was introduced for political as much educational reasons remains in place, but unloved by a government that is too weak to remove it. And while we lack robust evidence about its impact on education, it risks becoming an increasing burden on already stretched school budgets.