In relation to how often the MOT Testing Station Quality Control (QC) checks should be carried out, the MOT Guide states:
The frequency of checks may typically be expected to be 1 per tester every 2 months. However, this is based on the average garage throughput of 2 to 3 tests per day for experienced testers – so should be varied to reflect the volume of tests done or any other special circumstances – such as the experience of testers. For example, if a tester is inexperienced or doing twice the average of 2 to 3 tests per day you should consider increasing the checks to once a month.
We would strongly recommend carrying QC checks for all testers on a monthly basis.