Evaluation and Parts Certificate do not have validity by themselves. Whether or not they can be used under an EU-TEC or TEC that is valid in the UK depends on the availability of the documentation. This includes all design documentation, test reports and production documents. If you own the Evaluation of Parts certificate yourself, you have guaranteed access to this documentation, and you can use the certificate under an EU-TEC or TEC that is valid in the UK. Evaluation of Parts certificates that you do not own have to be evaluated case by case.