At the moment, the only thing you need to do is choose how to advertise
There is no legal requirement to be qualified.
However, taking things further, a lot depends on what you want to do.
DiaMond have their own bike examiner qualification course
RoSPA have the Diploma course
IAM test pass and 'observer' qualification might be a lnger-term but cheaper option, then use the skills to instruct
Basic/L skills are useful for trainees with poor basic skills
If you're looking to work very long-term, then the DSA's RPMT qual. will be needed. There are providers for this, budget for £1k + a week off work. The DSA may [should be?] able to point you at a full list (there may be more than one) of accredited training centres.
Advantage of RPMT is that DSA are - currently - funding serious amounts of advertising. However . . . whether that wil continue . . . ?
Alternatively, you could do it the 'ADI' way, by taking the theory, riding, and instructional ability tests via teh DSA.
UK Advanced used to run an instructor training course, don't know if that's still going.
For high speed skills, with a bit of work on transfering them on-road, the CSS L1 course might be worth attending.
Whereabouts are you, how much do you intend doing (full time, part time, 'hobby') and what is your current level of experience and training?
Edit: I'm guessing from your post that you're not currently involved in any training. In which case, join the DIA to get public liability / indemnity insurance when you do start training - whether or not you go down the DiaMond route.
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