Pupils are being urged to stock up on junk food at break times to avoid Jamie Oliver's healthy school dinners purge in English schools, it has emerged.
Jamie Oliver's campaign has seen sugary snacks banned
New rules brought in last month following a campaign by the TV chef ban the sale of crisps and sugary snacks.
But until next year the guidelines only cover lunchtimes.
And there is evidence schools and catering firms are encouraging pupils to buy their crisps and chocolate bars at morning break instead.
A notice posted next to the cash registers at one South London school appears to advise tuck shop staff how to exploit the new rules.
It says the school will "not be selling crisps and/or sweet snacks with chocolate in at a lunchtime period... only plain, still water, fruit juices, Capri Sun 100% and milk and yoghurt based drinks can be sold at lunchtime".
It adds: "Therefore it will be advisable to buy your drinks and other products at morning break."
The notice, seen by the BBC, states the advice has been agreed after consultation between the school and its catering firm.
The government's school dinner guidelines, issued last month, ban the sale of confectionary and crisps and say children should be given healthier options, such as fruit and vegetables instead.
The guidelines will not become law for meals other than lunch - including food sold at mid-morning break services, tuck shops and after-school clubs - until next September.
But the government has told schools it still wants to see the new standards introduced in tuck shops and other non-lunch outlets "as soon as possible".
School catering companies have come to rely on vending machines and tuck shops as a big source of profits.
Some have been demanding compensation for abandoning junk food sales.