Schools have been told to consider "lock-ins" at lunch-time to stop pupils going out and buying junk food during the midday break.
A survey by the School Food Trust, the agency set up by ministers to encourage healthier eating habits among schoolchildren, found secondary schools have an average of 23 junk-food outlets within a mile of the school building.
As a result, it is recommending that all schools look into the feasibility of introducing a "stay-on-site" policy during lunch-times.
The agency also wants local education authorities to adopt a stricter line on issuing licences to junk food outlets to operate in or near schools.
Judy Hargaddon, the chief executive of the School Food Trust, said: "At the moment school canteens have to compete with a myriad of takeaways, chippies and sweet shops for pupils' dinner money.
"We all know that some children will go for chips five times a week if they are allowed to. The problem is that this is damaging their long-term health and is also threatening the viability of school lunch services."
The survey showed that the number of junk food outlets within easy reach of secondary schools ranged from 46 outside Brighton schools to 11 outside those in Windsor and Maidenhead.
Several secondary schools are already operating "stay-on-site" policies to help encourage healthy eating habits. Alex Thomas, the headteacher of St Augustine's High School in Westminster, which has such a policy, said: "There are a number of junk food shops in our area and we were concerned about the number of pupils eating junk food at lunch-time and the effect that it had on their behaviour post-lunch."
Leicester City Council has also taken up the trust's second recommendation and banned mobile burger outlets and ice-cream vans from operating outside schools.
Robert Wann, a Leicester city councillor, said: "Schools in our area have been working hard to provide healthy, tasty food that gives kids the nutrition they need to get the most out of the school day.
"All too often their efforts are being undermined by a couple of burger vans parked outside the school gates doing a roaring trade. Hopefully, that will soon be a thing of the past."
The School Food Trust was set up as a result of the campaign by the celebrity television chef Jamie Oliver – through his Channel 4 TV series – to improve the standard of school lunches.Reuse content