FOOT-AND-MOUTH last night tightened its grip on Britain as it emerged that up to 25,000 animals could have already come into contact with the disease.

The list of abattoirs and farms known to have animals with the disease reached 12, with almost 7,000 sheep, cattle and pigs already culled or earmarked for slaughter.

And Government experts revealed that up to 25,000 animals may have been infected at markets before the ban on moving livestock was imposed.

In the wake of the crisis, the pro-hunting Countryside Alliance yesterday postponed its planned march, which had been due to take place in London on March 18, until at least early May.

Chief executive Richard Burge said the move had been taken as a precaution, following consultation with farmers' groups.

The outbreak has also threatened sporting events, with the Irish Rugby Football Union considering cancelling Saturday's Six Nations clash with Wales. There were also calls for the Cheltenham Racing Festival to be postponed.

The Irish government said it might call on rugby and horseracing fans to stay away from both events.

Prime Minister Tony Blair yesterday pledged the Government would take all necessary steps to combat the outbreak, which has already brought havoc to the countryside.

He said: "We have simply got to wait and see how widespread this disease is. Whatever is needed to tackle and eradicate it, those steps we will take." He also suggested that the Government might widen the compensation scheme for farmers. At present, cash is only paid out for animals which have to be slaughtered.

''We understand that there is more than simply the problem of the value of the animals slaughtered . . . we will certainly look at all these consequential losses," he said.

Investigations into the source of the outbreak are still concentrated on the Northumberland farm owned by brothers Ronnie and Bobby Waugh, at Heddon-on-the-Wall.

Among the additional cases confirmed yesterday was a farm at Westerhope, near Newcastle, where the disease is thought to have been carried by the wind. The farm -the third in the North-East confirmed to have livestock infected with foot-and-mouth - is only four miles from the Waugh's farm.

Ministry of Agriculture officials are now trying to trace animals which have been through auction marts in Hexham, Northampton and Longtown, in Cumbria.

Livestock hauliers are also facing checks from officials trying to determine where affected animals have been taken.

National Farmers' Union leader Ben Gill, who farms at Easingwold, in North Yorkshire, met the Prime Minister in Downing Street for talks yesterday.

He was reassured that the Government was committed to tackling the crisis and repeated his call for people to stay out of the countryside.

Mr Gill said: "In this extremely worrying situation it is helpful for the industry to have such reassurances from the Government that no efforts will be spared to rid the country of this terrible disease."

Local authorities have cancelled refuse collections at farms to try to halt the spread of foot-and-mouth and the National Trust has closed properties across the region, including the deer park at Studley Royal, part of the Fountains Abbey world heritage site near Ripon, North Yorkshire.

David Curry, Tory MP for Skipton and Ripon, called for the closure of rights of way in North Yorkshire, claiming they had been heavily used at the weekend, despite appeals to stay away from farmland