Britain could lose its beef export markets unless more care is taken over BSE checks, industry sources have warned.

When the export market was reopened last May the UK industry promised all cattle born before the end of July 1996 would be processed through the Older Cattle Disposal Scheme

and none would enter the food chain.

But between four and six older cattle a week - 250 in total since last May - have been detected by checks at abattoirs after mistakes made by farmers.

The number of OCDS cattle at food chain abattoirs has been increasing, according to the National Beef Association. "People are noticing these breaches and they have to stop," said NBA chief executive Robert Forster.

"We've heard rumblings from Defra of an unwelcome response from Brussels," he added.

The NFU urged farmers to take care when sorting and presenting cattle for slaughter.