A first aider is…
someone who has undergone training, and has current first aid certification, that is approved by the HSE. They must therefore hold a valid certificate in either:
First Aid at Work (FAW), or
Emergency First Aid at Work (EFAW).
In each case, these certificates must be issued by a training organisation approved by the HSE, or in the case of the EFAW, this can also be awarded by a recognised awarding body of OfQual / Scottish Qualifications Authority.
You should use your risk assessment to determine whether your first aiders should hold the FAW or the EFAW certificate.
HSE strongly recommend that all first aiders undertake a refresher First Aid at Work course annually.