So much for compassionate Conservatism. So much for helping the “just about managing”. During my time as deputy prime minister, I repeatedly blocked the Conservatives from proceeding with tax, welfare, education and pensions policies that did not cater for the neediest in society. I became wearily familiar with the Conservative party’s habit of placing greater priority on the needs of “their” voters than those of society at large.

Indeed, it was the Conservatives’ insistence in 2013 on going ahead with a “marriage tax break” – an expensive gimmick much loved by Conservative newspapers but of little use to most people in Britain – that prompted me to look for a measure that would do more to help hard-pressed families across the country. That was the genesis of our decision to provide healthy, free school lunches to nearly 2 million children in the first three years at primary school.

It’s less than a year since Theresa May stood outside No 10 Downing Street and declared that her mission was to lead a country that worked for everyone. Now that we know she wants to scrap universal infant school lunches – a measure proven to boost health and educational outcomes – while spending huge amounts of taxpayers’ money on new selective schools – a measure proven to damage social mobility – that statement looks hollower than ever.

It’s a cruel choice because it will hit children from some of the most deprived families in the country. Has the prime minister not read the evidence? At the time this policy was introduced in 2014, four in 10 children who did not receive free school meals were officially in poverty. It is these children who will lose out again.

The claim that they will instead benefit from the introduction of free school breakfasts does not stack up. Fewer children will benefit. Don’t take my word for it: the Conservatives themselves admit this in their manifesto. They estimate that the level of savings from withdrawing the lunches will be £650m – almost exactly what it cost to introduce the policy in the first place – so they clearly don’t anticipate that there will be much new demand or cost for breakfasts.

In any event, breakfast clubs, taking place outside the formal school day, tend not to reach the hardest-to-reach children. School lunches, shared by all children in the middle of the school day, do.

Yes, means-tested families will still get free school meals, but those who don’t qualify will have to pay huge bills. At present, the government subsidises each school lunch to the tune of £2.30. The decision to remove the free lunches will mean working families have to spend around £480 extra per child each year. For a family with two children under seven – in Year 2 and below – this amounts to almost £1,000 a year.

Just two years ago, the Conservative manifesto for the 2015 general election promised to keep the free lunches

Removing the universal provision also acts as a disincentive for many low-income parents going back to work or hoping to work more hours. Doing either will now mean that their sons and daughters may lose the entitlement to a free school meal. This directly contradicts the Conservative rhetoric on boosting incentives to work.

Just two years ago, the Conservative manifesto for the 2015 general election promised to keep the free lunches. Many of the Conservative MPs who stood on that manifesto had previously voted, under the coalition, in favour of the legislation to introduce the free meals in the first place. Now they are standing on a manifesto to take them away, reverse their previous manifesto and undo the legislation they previously supported.

So a simple question must be asked of every single Conservative candidate in every constituency: will you file through the lobbies to take away free lunches from the children of some of the most hard-pressed families in the country? Or will you stand up to your leader, and stop the Conservative party from becoming the party of lunch snatchers?