The bad bit of this is that whereas you are obliged to keep proof for JPA for 2 years, HMRC can tap your shoulder for 6 years.
This particular case falls into a grey area. You cannot claim any variation of home to duty, and as a rule of thumb, only claim journeys to and from a specific task. However a course on face value is no different from, for example, a symposium or conference. There is an argument that suggests the first journey to and last journey from are fair game but others are because you yourself choose to do them and therefore you pay.
My advise would be to stick with topping up the service journeys only (up to the JMRC rate of 45p/mile ) and avoid the risk associated with GYH. That said, if a claim is wrongly put in in good faith, the worst that can happen is that you pay it back. HMRC may smell a rodent if you are claiming the full 45p per mile. You have of course said you got GYH throughout, but you didnt say that this was as if you remained at home base. I would be careful with that as psf have a get out of jail free card whereas you do not.
I do pay an accountant and he always saves me far more than his bill, and he would check on this if it were my claim before executing the claim. Everything that I have claimed in recent years has been supported by a JPA claim in which evidence of mileage was beyond all doubt. You will not have this if you are not entitled through service means to claim mma.