Farmers and country landowners are demanding action following the revelation that the devastating swine fever outbreak could have been caused by a walker's discarded sandwich.

The Country Landowners' Association (CLA) and a leading pig breeder in the North Yorkshire area want walkers to be more aware of the risks they could be introducing to livestock by discarding food and wrappers on public rights of way through farmland.

Dorothy Fairburn, regional director of the CLA in Yorkshire, said her group was urging the Government to consider the case as the Countryside and Rights of Way Bill, designed to introduce the right to roam, enters its committee stage in the House of Lords.

She said: "What is really worrying is the view that the first infected pig possibly ate a sandwich containing infected meat discarded by someone on a footpath alongside part of the pig unit.

"At committee stage in the Commons, the CLA supported an amendment which would make it an offence for anyone exercising the new right of access to feed animals, but it was rejected."

Matthew Atkin, chairman of the British Pig Industry Support Group, who farms at Pocklington, near York, said he was keen for the Government and the Ramblers' Association to have more flexibility over the issue of temporarily closing footpaths when there is thought to be a risk. He said: "At the moment, we're not allowed to close footpaths until we get swine fever, which really is shutting the stable door after the horse has bolted.

"The Government ministry should be sufficiently flexible to allow temporary closures of footpaths to prevent the spread of diseases and there should also be more flexibility from the Ramblers' Association."

A spokeswoman for the Ramblers' Association said today it was impossible to be so certain about what had caused the swine fever outbreak. "It could have been anything," she said.

reporters@ycp.co.uk