How do you mean designated alphabetically from the front? Do you mean like people are situated according to their surnames? I am quite sure that is not the case. The cars are booked out from the centre to the front and then to the back (I think). Seats are numbered with the higher number at the front end of the carriage and seat number one at the rear of the carriage.
Yes they are numbered from the front of the set. A at the beginning (business) to F at the end. Seat 12 would be situated towards the ends of the carriages. In car C the numbering starts from 66 at the front and 1 at the end. In car E I think the seating starts from 33 at the front to 1 at the end.
Hope this helps,
PS What day are you travelling up?
Have you looked at our flashy new Photos section yet? You can browse by author, locomotive, loco class, livery, country, region, decade, and a lot more!