Just a thought, and I am in no way connected with JPA etc, but could the new "automatic" mean that, rather than using the manual method of working out how far you drive to work each day
Don't think that's what 'automatic' is - having started looking to moving Melchett Towers outside the wire and one of the things I checked up on was HTD as as has been mentioned, most of us have fairly lengthy commutes. From what I could make out, the automatic rate is what you get when your HTD is automatically paid as part of your monthly salary whereas the manual rate is what you get for ad hoc journies which you have to claim for.
I think the manual rate is more because you are limited as to how many times you can claim it each month.
Well that's from what I could make out from the scribbly bible, but to be honest it may as well have been written in Swahili, so someone may actually have a better / correct explanation than I can come up with.