Investigators in  the UK are reported to have found donkey DNA at two firms raided last week as part of the horse meat probe, indicating that beef food products were contaminated by not just horselesh, but donkey meat as well.

The Daily Mirror reported today that donkey DNA was found at the two sites, along with samples of donkey and horse meat. The newspaper quoted sources close to the investigation.

Dozens of polythene bags containing a mixture of beef, horse and donkey meat, meant for export were seized by investigators, the reported said.

The samples are undergoing analysis at a government-run lab near York as part of the on-going UK Food Standards Agency probe into the ­illegal supply of contaminated beef.

Donkey Sanctuary charity spokesman has called the claims, ''shocking''.

While the slaughter and trade of donkeys was not illegal, the allegations raised fears the meat could have found its way into British shops.

Meanwhile, UK Border Agency customs officers have seized 48 tons of illegal meat including horse and donkey in the last seven years, according to The Daily Record.

Seizures had been made at London's Heathrow and Manchester airports, Tilbury docks in Essex and Liverpool docks.

The illegal meat was not cleared for human consumption and was later destroyed. There were also fears it could contain diseases.

Customs officers have been on alert after the outbreak of foot and mouth disease in Bulgaria two years ago.