The UK's Food Standards Agency has insisted the traceability systems in place to track ingredients down the supply chain are proving robust as it works to uncover how undeclared horse meat made its way onto frozen beef products.

"We are using the traceability systems to trace back," a spokesperson for the FSA told just-food today (11 February). "This is a complex investigation with many strands. It does take time."

The FSA launched an investigation last month after its Irish counterpart revealed tests had detected horse meat in frozen beef burgers on sale at a number of retailers in the UK and Ireland, including Tesco, Aldi, Lidl and Dunnes Stores.

The scare has since drawn in branded food manufacturer Findus. Last week, the company was forced to recall its products, including lasagne, that tested positive for horse meat in France, the UK and Sweden. The lasagne was manufactured by French group Comigel.

The Food Safety Authority of Ireland has suggested the horse meat in beef burgers originated from Poland. Meanwhile, French authorities have claimed the horse meat in lasagne came from a slaughter house in Romania.

The UK's FSA is yet to make a statement on what it thinks is the source of the tainted meat. "Our investigations are continuing about the source. We haven't speculated," the spokesperson said.

In a bid to ensure no more products on UK shelves contain undeclared horse meat, the FSA has required food retailers to test product and report back to the safety watchdog on Friday. The agency is holding a technical meeting with the industry this afternoon to discuss the "testing and detail".

The FSA spokesperson said tests would be performed on products deemed to represent the greatest risk first. Based on the initial results, the FSA will then make a decision on whether further tests are necessary.