More than half of all Sussex primary schools lack proper kitchen facilities and several give pupils meals on wheels every day, the Tories have claimed.

Figures obtained by the Conservative Party under the Freedom of Information Act showed that just 200 (42%) of the county's 470 primary schools had "full production" kitchens.

Many relied on "mini" kitchens to reheat pre-prepared food, dozens served only cold food while a further 25 were forced to wheel meals in from other schools.

West Sussex primaries were the worst kitted out in the county, with only five out of 243 (2%) being fully equipped. By contrast, most schools in East Sussex (83%) and Brighton and Hove (91%) were capable of providing fresh, hot meals on site.

A spokesman for West Sussex County Council said £5.7m was being spent on new facilities and upgrades to provide its schools with mini-kitchens to heat food using "steam pressure".

It said its new steam systems, introduced since 2007, ensured food retained its "maximum nutritional goodness" and met all Government standards even though it was not made freshly on site.

The statistics were revealed as tougher nutrient standards were made mandatory in secondary schools, and two pilot schemes to provide all primary school children with free, healthy lunches every day throughout the school year were launched in East London and County Durham.

The two-year trials will be evaluated, which could lead to them being rolled out to other areas in the future.

But the Tories said their survey of local authorities threw into doubt the possibility of extending free and healthy meals to all primary school children.

Across the country, they discovered, three in 10 primaries do not have full kitchens, with 19% transporting food from another school and some 670 schools (4.5%) serving only cold food.

Shadow schools minister Nick Gibb, Tory MP for Bognor and Littlehampton, said: "The idea that the Government will be able to find the extra £1bn a year that it's estimated would be needed to pay for such a scheme to go nationwide is completely unrealistic in the current economic climate.

"£1bn is the equivalent of 33,000 full time teachers, they would effectively have to stop all teacher recruitment in order to pay for it, regardless of the fact that one in five primary schools don't even currently have a kitchen."

But Schools Secretary Ed Balls, reacting on social networking service Twitter, said: "Just a pity the Conservatives are opposing the free school lunch pilots and won't support our nutritional standards for healthy eating."

Mr Balls said earlier: "Eating a nutritious meal at lunchtime from a young age can help improve the behaviour of children in school and at home - that's why these pilots are so important. Healthy school meals are vital to helping children do well at school and to prevent obesity."