Tudor Griffiths, of Kettlethorpe High School, said £20,000 of his school budget was spent each year trying to ensure pupils ate healthily and were not tempted by rubbish.

But he said the lure of cheap sweets and treats at Asda, at nearby Asdale Road, was proving too much of a temptation for some children, who were sneaking out at lunchtime to satisfy their cravings.

And in extreme cases, some entrepreneurial pupils bring the temptation back to school by bulk buying chocolate and pop to sell to their peers for profit.

He said: “We have removed all our vending machines and introduced smoothies and water coolers, as well as healthy lunches. All this is often at a cost to other things in school like trips and events, so it is very frustrating.

“We are lucky in that we don’t have fast-

food outlets on the doorstep, but we do have Asda and I really would like to see them take a more responsible position on this.”

Last week the Express revealed shocking figures released by the School Food Trust, which showed Wakefield had the highest number of takeaways and sweet shops per secondary school in West Yorkshire.

The trust hoped naming and shaming the areas providing pupils with the ‘most temptation’, would help persuade schools to close their gates at lunchtime and get councils to stop new fast food shops setting up nearby.

Mr Griffiths said pupils were not allowed to leave the Standbridge Lane school during the day without a pass, and even then, the permit only allows pupils to go home.

He said: “They are not allowed to go to Asda and it is something we take a strong stance against. In the past we have had staff going over and rounding them up, but we are fighting a losing battle.”

But he said 80 per cent, about 1,200 of his pupils, used the school’s dining facilities each day, where they are awarded points for making healthy choices, with prizes going to the healthiest students.

A spokesman for Asda said: “We take healthy eating very seriously, which is why we have removed 400 tonnes of salt from our products and we were the first supermarket to remove all artificial colouring and additives from all our branded products.

“Therefore, we support Kettlethorpe School’s work to encourage healthy eating, but it would be difficult to set aside time for colleagues to police the entrance for pupils at certain times of the day.

“If the headmaster would like to visit our store, we would be happy to discuss further.”