What STO did not mention was that you can claim back up to about 5 or 6 years.
Also you do not have to claim only the SAMA paid rate.
For instance the regulations state that you could have used trunk roads as that is government policy and not the AA shortest route basis. Had you undertaken a journey that involved the M1/M25/M3 or M4, handbrake house may have paid you the direct route. Say that was 125 miles but the motorway route was 150 then you could claim the 40-ptr for 125 miles and 25 miles at the full 40p/m.
You can also claim for non-htd journeys for which you had no SAMA claim. For instance Mrs Dog may have driven you to the rail station which was within your htd radius and handbrake house did not pay a claim. Then that is claimable at 40p per mile for 4 journeys as your car made the return trip each time.
Did you know that handbrake house would pay these return trips if you claimed?
Did you ever do a course where you got mileage for the outbound trip in week 1 and homeward in week 2? Well you can claim the tax relief on the return journeys in between.
I was challenged once by the compliance unit who alleged that I was recompensed by the MOD. The rules had just changed and they were not up to speed. I pointed out the regulations and that I was simply claiming the difference. I did not have to send any paperwork nor did I have to detail the journeys.