Any laboratory which becomes UKAS accredited to ISO 17025:2005 must demonstrate its ongoing competence by participating in an appropriate Proficiency Testing scheme such as FAPAS (for food Products) or CONTEST (for Contaminated Land samples).  

Participation in a proficiency testing scheme is mandatory if UKAS accreditation is to be maintained.

Samples, spiked with unknown levels of compounds, are sent out three or four times a year to the accredited facilities. Laboratories must analyse the samples for the specified analytes and report the results back to the PT Scheme Coordinator (Central Science Laboratory for FAPAS, Laboratory of the Government Chemist for CONTEST)

 Each participating laboratory subsequently receives a Report containing the results from all participants

An individual laboratory which has participated in the scheme is provided with a code enabling it to identify its own performance. It is NOT able to specifically identify any other laboratory's results by name.

Individual results are assessed against the mean value that is set by the scheme coordinator and the results are deemed ‘acceptable' if their statistically calculated Z scores are within < 2 > of the mean value.

At the annual inspection by UKAS, the laboratory's results from each Round will be assessed for ongoing competence and consistently poor results could result in a particular method being removed from the Accreditation Schedule.