Primary school prices ranged from 95p to �1.65

The union also found school dinner provision was coming under threat with only 13% of local education authorities providing a service in middle and secondary schools, while 63% had cafeterias instead.

Unison based its findings on a survey of 83% of local education authorities in England, Scotland and Wales and published the results to coincide with National School Meals Week.

The most expensive place to buy a primary school meal was in Wandsworth, south London where the cost was �1.65.

The cheapest place for a primary school meal was Dumfries and Galloway, which charged 95p.

Secondary school

For a secondary school meal, pupils paid most in Edinburgh and in the London borough of Bexley, coughing up �1.85 for a hot dinner.

Dumfries and Galloway was again the cheapest place at �1.

Pupils in middle schools in Norfolk and Northumberland paid the most for their meal at �1.55 while pupils at these schools in Islington, London paid the least at �1.15.

In its last survey in 1995, Unison found prices in primary school ranged from 65p to �1.25 and from 65p to �1.50 in secondary schools.

'Commitment'

"Unison wants to see a solid commitment to a national, comprehensive school meals service which is adequately funded and puts our kids on the road to a healthy future," said Unison general secretary Dave Prentis.

"We are particularly concerned at the dramatic drop in the number of authorities providing wholly in-house services," he said.

Unison has many "dinner lady" members who used to work for LEAs but are now often employed by private companies as school meals services have been increasingly contracted out.

"We know that the impact on staff of contracting out is mostly a negative one and that new starters on contracts are often employed on inferior pay and conditions," he said.