One of Britain's leading vets says the most likely cause of the foot-and-mouth crisis was infected meat imports that ended up being fed to UK pigs.
Comments by Professor Mac Johnston are backed by other vets who say the disease crisis highlights problems in the meat supply chain.
It was only down to "luck" that Britain had managed to avoid infection for so long, added the professor.
The last outbreak of foot-and-mouth disease in 1967 was eventually traced to an imported joint of meat.
Foot-and-mouth can be harboured in the lymph nodes of an animal, which are trimmed from imported carcasses after arrival and can end up in pig swill, said the professor.
He added: "The virus will not survive in meat for more than two weeks if it is healthy. But it can live in the lymph nodes, which filter toxins from the bloodstream, for four months."
Recent problems in the domestic meat industry - such as BSE and an outbreak of swine fever last year - had made imports more economically attractive, he said.
The professor said it was "worrying" that nobody had quantified the scale of illegal imports of meat into the UK.
He said: "Why is it that swine fever affected mainland Europe over several years in the second half of the 90s and we did not get it, only to get hit by two different diseases in a year?
"Luck has kept it out."
'Virulent' strain
Professor Philip Duffus, of Bristol Veterinary School, agreed that pig swill was a possible source of the infection.
"I think we should stop feeding swill to pigs and stop importing from countries with infection," he said.
He said the "virulent" virus in Britain was similar to one which affected South Africa recently and was the same type 'O' strain as that which caused an outbreak in Japan.
The source of the outbreak would eventually be traced by analysing the molecular composition of the virus, Prof Duffus added.
Cheap food - who pays?
Julie Briggs, of Compassion in World Farming (CWF), said there was a need to "radically" reform agricultural practices.
She said: "We need to look at reducing journeys and improving intensive farming practices so that animals are not kept in close-packed environments where they become stressed and therefore susceptible to disease."
CWF has launched a campaign this week calling for widespread reform of agricultural practice, called Cheap Food, Who Pays The Price?
It calls for an urgent review of Britain's cheap food policy, an end to intensive farming practices, more support for farmers to encourage welfare-friendly practices, a ban on live exports, and shorter journeys to slaughter.
It also asks consumers to take more responsibility for what they eat.