Schoolchildren may have been served horsemeat in their lunches.

Yesterday a catering giant that supplies food to schools, care homes and the armed forces withdrew nearly all its beef after a frozen product tested positive for horse DNA.

Sodexo said the situation was “totally unacceptable” and the products were being recalled “with immediate effect”.

The company supplies school food to St Wilfrid’s Catholic School in Crawley.

It also manages the catering at Hurstpierpoint College, although a school spokesman said all food was sourced from local suppliers.

Sodexo has launched an investigation into how beef products were contaminated with horse.

It said its Tillery Valley Foods business – which supplies meals to Brighton and Hove City Council and Brighton and Sussex University Hospitals – was not affected.

Last week, burgers were withdrawn from school menus in Brighton and Hove as a precaution as the scandal of horsemeat in the food chain grew.

Brighton and Hove City Council insists there is no evidence that beef products given to children have been contaminated, but it has dropped Red Tractor burgers until it gets guarantees from suppliers.

It also emerged that horse DNA has been discovered in lasagnes and beef burgers by the suppliers of food to hotels and restaurants across Sussex.

In the latest Food Standards Agency test results, out of 1,133 meat products checked, only six – including Sodexo’s beef burgers – were positive for horse.

In a statement, the firm said: “Sodexo has had a proactive programme in place to ensure that there is no horsemeat in its supply chain.

“We demanded written assurances from across our supply chain that the products we purchased did not contain horsemeat, and additionally implemented an internal sampling programme.

“Despite repeated guarantees from our suppliers, our sampling has identified a frozen beef product which tested positive for equine DNA. This situation is totally unacceptable.

“We felt the only appropriate response was to withdraw not only this product but all frozen beef products.

“We will only re-admit into our catering operations products that have affirmatively passed DNA testing, pursuant to laboratory test criteria.”