I wouldn't get your hopes up, I know plenty of tech spankers all the way up to 3 bananas who still don't hold a full UK driving licence as its not trade essential... If I were you I'd just be grateful for place at Arborfield.... I'm sure I've heard they're reducing their numbers! I'd save your pennies and do it yourself... or join the RLC.
I know of very few people that have come out of Arborfield without at least their Cat B. I already had mine before transferring but managed to get my cat C while there. Most guys are doing their cat b in any gaps in training then going to Leconfield/Bordon for their C/C+E either just before or shortly after going to unit. Guys in my Bn that have not got their Cat C are being sent to Folkestone to get theirs so most guys have them, especially with us having just covered WRP and 3 Prairie Thunder Exercises, then ramping up for Herrick next October.
To be a class 1 tech you should hold a car licence and C, C+E, however some times they just dont care, you my get it or you may have to wait till your first unit and try and get it sorted. I know plenty of people who never got their B license never mind their C, C+E. It depends on how they are feeling at the time.