For this tax year a benificent Treasury has increased the car allowance to 63p.
Regarding not being able to claim for training, I claimed for any journey for which I got the lower rate PMA. I was audited when the rukes first changed and the rate for large cars was 63p. I had just bought a 2.5l car and done considerable mileage on resettlement. The Inland Revenue allowed all the claims.
Your mileage claim can also cover the journey actually made and not the journey paid by JPA. For instance an authorised journey and allowance for 100 miles claimed. Route actually used - traffic - faster - got lost - etc 120. You can claim the 100x40 - 100x25 plus 20x40.
One final wrinkle, Mrs drives you to the airport and drives home - you can claim the total mileage and not the one-way. I have also claimed (unchallenged) for the same return journeys to rail stations. You can claim (or you could) 3-years on unit and up to 6 years but needed to get the records from archives if you have never claimed the double journey.
I got that tip from a very nice lady at ISL, the complete opposite of her counterpart at ISK. Check QRs carefully; amazing what you can find.