The horse meat scandal has highlighted the tortuous supply chain of the ingredients used in some cheap British food products.
Supermarket giant Tesco, frozen food firm Findus and budget store Aldi were supplied with products containing horse meat by Comigel, based in north-east France.
Comigel instructed Tavola, its subsidiary in Luxembourg, to make the products. Tavola placed an order for the meat with Spanghero, in the south of France, which contacted a Cypriot trader, who subcontracted a Dutch trader.
The Holland-based company placed an order with abattoirs in Romania, which sent the meat to Spanghero.
The Doly-Com abattoir in the village of Roma, northern Romania, opened its doors to the media in a bid to demonstrate its innocence.
The company has said the meat was properly declared and any mislabelling occurred elsewhere.
Comigel's factory in Luxembourg received the meat from Spanghero, and it was used in food products sent to stores across Europe, including the UK.
Previously, it seemed meat linked to the scandal was thought to have come from continental European suppliers.
But for the first time it appears the contamination could also stem from British premises, with the Food Standards Agency (FSA), accompanied by police, raiding two British processing plants.
Peter Boddy slaughterhouse in Todmorden, West Yorkshire, and meat processing plant Farmbox Meats at Llandre in Aberystwyth, West Wales, had records seized and were temporarily shut down pending the outcome of investigations into claims they supplied and used horse carcasses in burgers and kebabs.
The FSA said it "detained" all meat at the premises and seized paperwork and customer lists from the companies.
The news came as Waitrose announced it had withdrawn its beef Essential British Frozen Meatballs after pork was bound in two batches.