Four beef products sold by Bird's Eye, Taco Bell and catering supplier Brakes have been found to contain horse DNA, the Food Standards Agency says.
This is the third wave of test results received by the FSA, which has now received a total of 5,430 test results.
Meanwhile, new tests conducted on beef retail products revealed no new cases of horsemeat adulteration, the British Retail Consortium (BRC) has said.
This latest round of tests saw 1,797 products being examined.
The FSA has asked retailers to test beef products for the presence of more than 1% of horsemeat, with anything above that figure considered to be a sign of adulteration.
Its latest results have found that more than 99% of tests show no horse DNA at or above the level of 1%.
The affected products are Birds Eye's Traditional Spaghetti Bolognese and Beef Lasagne - which the company took off shelves last week as a precaution; Brakes' Spicy Beef Skewer; Taco Bell's Ground Beef.
Taco Bell has three outlets in Britain and says all its affected stock has been removed. The products had come from a supplier in Europe, the company said.
A spokesman for Taco Bell said: "Once we learned of this issue, we immediately voluntarily tested our product for our three Taco Bell restaurants in the UK.
"Based on that testing, we learned ingredients supplied to us from one supplier in Europe tested positive for horsemeat.
"We immediately withdrew it from sale, and discontinued purchase of that meat and contacted the Food Standards Agency with this information. We apologise to our customers and take this matter very seriously as food quality is our highest priority."
Birds Eye said in a statement: "We are introducing a new ongoing DNA testing programme that will ensure no minced beef meat product can leave our facilities without first having been cleared by DNA testing."
Brakes, which is based in Ashford, Kent, said: "Our testing programme represents a significant proportion of all results the FSA has obtained from across the food industry.
"Brakes have also segregated a frozen burger as a precaution after equine DNA at 1% was reported to the Food Standards Agency."
It said it was "very disappointed to have been let down" by suppliers and that it "sincerely apologised to our customers."
Meanwhile, fast food chain McDonald's announced that none of its meat products had tested positive for horse DNA, adding customers could "continue to trust in the quality of food" served at its restaurants.
The BRC says 95% of its members' products have been checked, including all minced beef lines used by the UK's largest supermarkets.
There have been 361 tests on 103 products carried out since 22 February.
The trade organisation represents a range of retailers, including supermarkets and independent shops.
A total of 1,889 tests have been carried out by BRC members since 20 January, with 0.3% of them finding traces of horsemeat.
The BRC's food director, Andrew Opie said: "The UK's major supermarkets, and a number of other BRC-member food businesses, have now tested all existing processed minced beef products.
"The reassuring news is that another intensive week of testing has produced no new positive results. And, since this testing programme started in mid-January, just a third of 1% of products have tested positive."
Horsemeat was first discovered in January in frozen burgers on sale in the UK and the Republic of Ireland, and since then traces have been discovered in processed beef products and prepared meals across the EU.
A first wave of tests on beef products sold in the UK found horsemeat in some products sold by Aldi, Co-op, Findus, Rangeland and Tesco.
Subsequent rounds of testing revealed adulteration in some products sold by Asda, Sodexo - which supplies food to schools, care homes and the armed forces - and the Whitbread Group.
Last week Ikea withdrew a batch of frozen meatballs from sale in the food section of stores in the UK, and other European countries, after tests in the Czech Republic found traces of horsemeat in those products.