Coalition deal means free school meals for every pupil up to year two - and tax breaks for married couples

Nick Clegg to announce £600m plan for children while deal with Tories gives green light to long-awaited tax breaks for married couples

An estimated four in 10 children who qualify for free meals do not claim them (Rex)

All five-to-seven year-old pupils in state schools in England will receive free school meals from September next year, Nick Clegg will announce today.

The £600m plan is designed to boost the health and educational attainment of children, and will save families an average of £437 per child per year at a time when many are struggling with the cost of living. It will be unveiled in Mr Clegg's speech to the Liberal Democrats' conference in Glasgow.

In a Coalition trade-off, the Lib Dems have given the go-ahead for the Conservatives to announce a long-awaited tax break for married couples, possibly at their conference in two weeks. It will cost a similar amount and could be worth about £3 a week.

Providing a hot, healthy lunch for an extra 1.5m children means that better off families will benefit, which will raise eyebrows at time when welfare has been squeezed and child benefit cut. Some 400,000 children already receive free meals but an estimated four in 10 children living in poverty do not qualify.

Mark Littlewood, director general at the Institute of Economic Affairs, said: "This is an enormously bad use of public money. Not unreasonably, the Government already ensures that those in need have access to free school meals, so it beggars belief that we are now going to see a policy instated which will subsidise the children of affluent families."

However, universal meals for all primary school pupils were recommended in July in a review which found that in pilot schemes, students were two months ahead of their peers academically when free lunches were provided. The number eating vegetables at lunch rose by 23 per cent, while the number eating crisps dropped by 18 per cent. The improvement was most marked among children from less affluent families. Their progress in maths and English was more marked than that which followed the introduction of a compulsory literacy hour in 1998.

The School Food Plan was drawn up by Henry Dimbleby and John Vincent, co-founders of the Leon restaurant chain, who said "every word" was endorsed and "signed off" by Michael Gove, the Education Secretary.

The Deputy Prime Minister insisted: "It's my idea, it's a Liberal Democrat idea. It's something I've been wanting to do for a long period of time. If we ever had the money, I'd like to go further and give all primary school children a good hot healthy meal at lunchtime." A pledge to extend it to all primary children may be included in the Lib Dems manifesto at the 2015 election.

In a year's time, the Coalition will provide free school meals to disadvantaged pupils in further education and sixth form colleges. At present they are only available for students in school sixth forms.

Mr Clegg said: "My ambition is that every primary school pupil should be able to sit down to a hot, healthy lunch with their classmates every day. We will start with infant school pupils because teaching healthy habits young, and boosting attainment early, will bring the biggest benefits. Universal free school meals will help give every child the chance in life that they deserve, building a stronger economy and fairer society."

Nick Clegg and his wife Miriam Gonzalez join a ‘healthy eating’ class at a Glasgow school (Getty) (Getty Images)

Defending the decision to provide free lunches for meals for children from better off families, the Lib Dem leader said: "Sometimes you need to do things for everybody regardless - we are giving everybody help with paying their council tax, keeping fuel duty as low as we can, giving over 20m people help by raising the point at which they pay income tax. We are applying the same approach."

In today's speech, Mr Clegg will criticise the Tories' plan to reward marriage in the tax system. "A tax break for some, funded through the taxes of others. That tells you everything you need to know about their values," he will say. On Monday, the Lib Dem conference attacked the Tory tax break as "discriminatory, unnecessary and expensive."

Under the 2010 Coalition Agreement, the Lib Dems will abstain when the tax break is put before the Commons. George Osborne, the Chancellor, will announce how he will fund the £1.2bn a year of extra spending in his autumn statement later this year. Treasury sources suggested it could mean cuts elsewhere.

Anne Longfield, chief executive at the 4Children charity, said: " Providing a nutritious, hot lunch for all infants in primary school promotes positive eating habits and helps to ensure that children are able to concentrate and perform well in the classroom. It should also get over the stigmatisation that prevented hundreds of thousands of eligible families claiming in the past - a particular problem in some of the poorest, inner city areas of England."