The Food Standards Agency said the positive tests involved seven products sold by five suppliers, CNN reported Friday.
More than 10,000 products are still to be tested.
Half of the positive tests were for lasagna products sold by frozen food processor Findus that triggered the horsemeat alarm last week.
Authorities raided three United Kingdom food plants Thursday and arrested three people at two plants whose permits were revoked Wednesday.
Officials said shepherd's pie had been pulled from 47 school kitchens in northern England after DNA tests revealed the presence of horsemeat.
Catering giant Compass Group and Whitbread said Friday it was removing a meat lasagna and a beef burger from its menus after it found horsemeat in the products.
Companies that provide in-flight meals to airlines said they had begun reviews of their suppliers, asking for written confirmation their products do not contain horsemeat.
The European Union confirmed Friday that it would begin testing across all 27 member states.