"In addition to the cases of gross contamination there have been cases of trace contamination, " Ms Brown added.

BBC: Horsemeat scandal: Public quizzed on contamination

The results of FSAI tests, released to the UK FSA on 14 January, revealed some burgers made at the Silvercrest plant contained up to 29% horsemeat, constituting a "gross contamination".

BBC: UK

The FSA was using the 1% threshold "as a pragmatic level to determine the difference between gross and trace contamination", she said.

BBC: Horsemeat scandal: Public quizzed on contamination