It all depends on the quality and accreditation which comes with the course. There is unaccredited first aid for mental health trainers courses at low cost but with no standards and no accreditation, the certification would not be recognised by any UK awarding body. There is also the Mental Health First Aid Trainer England MHFA but this can be a few thousand for a trainers course. The best option is to do an accredited first aid for mental health trainer course from one of the UK awarding bodies. Abertay for example provides a 3-day SafeCert Awards Approved first aid for mental health trainer course at £375 + vat, but there are many companies who offer first aid for mental health instructor courses that can be anything up to £700 + vat.
The best practice is to search for a trainer’s course that is recognised by one of the UK awarding bodies, then you will be assured that the first aid for mental health trainers course has been fully quality assured and assessed for content.