Well you used to be told to do 'Front End Turns' which means shadowing a Driver (who isn't a DI) for their turns of duty, watching them drive, and learning as much as you can from day to day things and the routes you go over, which would keep you ticking along until a DI became available.
I think there may be an element of "Keep up the knowledge you've gained so far from home," at the moment with COVID.
You would still be getting paid.
In the past when the timetable in May 2018 went into meltdown, the training school closed for about three months whilst the Classroom Trainers were redeployed to keep the timetable holding up as best they could.
Trainees were delayed sometimes quite significantly during this period. Upon qualifying they received full Driver's rate backpay to roughly when they should've passed out. The delays to their training weren't their fault, and had the timetable difficulties been properly forseen, they would've been employed at a later date, rather than their progress being paused.
I think they may have got some of this payment earlier as some had left jobs that paid better than Trainee Driver and were starting to struggle financially as the estimated time that training should take had been and gone, and their banked on jump to Qualified rate was still not in sight.
I would recommend to join the union - ASLEF, as they were the ones negotiating this to help people.
Quite a lot of groups of Trainees create WhatsApp groups etc. to help each other with the learning and keep in touch through the training.
Uniform - if you are going for polo shirts, go at least one size up, possibly two even. They are tight on the arms.
You can always send stuff back if it doesn't fit. My polos went back twice, lol, for the next size up each time.