Tesco has apologised to shoppers after it discovered horse meat in a beef meatloaf manufactured in Northern Ireland.

The grocer said its frozen Tesco Simply Roast Meatloaf supplied by Eurostock in Craigavon in Northern Ireland had between 2-5% horse meat.

Tests on 15 other lines from the same manufacturing site were clear of horsemeat.

Tesco group technical director Tim Smith said: “Our investigation to thoroughly understand the source of the contamination has started and we will complete our investigation before deciding whether to continue using the supplier.

“As part of our new DNA testing programme we have now tested more than 500 products identified as being most at risk of containing horsemeat. This is the fourth Tesco-branded product to have tested positive.”

He added: “We are very sorry that we have had a further product which has failed to meet the high standards we and our customers expect.”

Tesco is among a raft of retailers to have discovered horse meat in beef products in the last two months.