Nice post 26 years an Lgv Trainer.
I am keeping a log of dates for my course at the moment. So for example a week tomorrow is the first date according to my last letter from Sterling that I can ring them up and hassle them for a date for my Cat C Course. They quoted an average of 5 weeks from Theory Pass to the actual Practical so under 3 weeks to go now. 
There is absolutely no mention in their T&Cās about having to take retests with them so if I fail I shall retest elswhere and then resume my course with Sterling.
If they give me hassle I shall not hesitate to toodle off to the Trading Standards dudes.