Sir: Although MPs are calling for supermarkets to be prosecuted for selling beefburgers that contain horse meat, the challenge of tracing the lines of liability will make action a real challenge.

Several potential food regulatory breaches are likely to have been committed, including misleading labelling. Working out which companies should be prosecuted, for what and in which jurisdiction, will be fraught with difficulty.

Not only was the meat processed from plants in Ireland - which is outside the jurisdiction of the UK’s FSA - the meat itself is understood to have come from elsewhere in Europe.

Regulators often steer clear of trying to prosecute organisations outside the country so, if the FSA deems that breaches have occurred, it is most likely that criminal proceedings would only be contemplated against companies actually operating in the UK.

Even if they are prosecuted, if the supermarkets can prove they carried out due diligence then they could escape criminal conviction. The supermarkets are likely to use the defence that, not only did they rely on information from others, but in respect of their own-label goods they also carried out their own checks. It could all come down to the extent of those checks.

Ian Mayers, partner at national law firm Mills & Reeve