No new cases emerged on Saturday, which Britain's chief veterinary officer Jim Scudamore said was a "hopeful sign".

A Maff official carrying a "humane" killer

The government has banned all transport of livestock throughout the country in an attempt to stop the spread of the highly contagious disease, which affects pigs, cows, sheep and goats, but is harmless to humans.

Mr Scudamore said the slaughter had begun not only at the six confirmed outbreak sites but also at two nearby farms.

The carcasses are also expected to be burned on Sunday.

Officials in Northumberland will decide on Sunday whether roads will need to be closed as the carcasses infected with the highly-contagious disease are burned.

At Burnside Farm at Heddon-on-the-Wall, suspected to be the source of the outbreak, diggers have been excavating holes for the fires.

'Cautious optimism

Richard Drummond, head of veterinary services for the northern region of Maff, said the disease had a three-to-four day incubation period and "the longer we go without any fresh outbreaks the better".

Activities curbed

Monday's race meeting at Newcastle is cancelled Camping and Caravaning Club cancels meets RSPB reserves closed Fox and deer hunting and hare coursing banned Whipsnade Wild Animal Park and Woburn Safari Park are temporarily closed Half of all city farms shut Visitors to London Zoo are being asked to walk across disinfected matting

Mr Brown has admitted supplies of meat will be disrupted but warned shoppers not to start panic buying.

Supermarkets said there had been no reports of people rushing out to stock up.

The use of the UK and EU's reserve of vaccine, which had been examined, were not the way forward, he added.

Mr Scudamore said herds of wild boar and deer would be examined if they were close to an outbreak and culling would be an option in the event of infection.

He said vets were being drafted in from across the country to help track the disease.

Maff officials will consider reports that pig swill could have been involved in triggering the outbreak. Children living in affected areas in Northumberland have been told by council chiefs to stay at home until further notice.

Maff officials now say the virus may have been spreading from the farm at Heddon-on-the-Wall for more than two weeks and could have been in the country for a month.

Farm owner Bobby Waugh, 55, says his premises, which had 500 pigs, were given a clean bill of health by Maff inspectors on two recent visits.

Mr Scudamore said he was satisfied veterinary officials had found no sign of the disease during a visit on 24 January.

There have been 16 suspected outbreaks of foot-and-mouth disease since the alert began at an abbatoir in Essex earlier this week.