Based on what you’ve said you’d have run out of time before getting back to the yard and as this was your 6th shift you’d have had to have parked up for a bare minimum 24 hours.
I wouldn’t say insisting you take a weekly rest in your cab is reasonable. I’d be looking at some sort of claim for unfair dismissal, even if you have no intention of going back.
And don’t let them deduct money from you, that’s nonsense. i had an employer deduct £480 holiday from me when I walked off a job one day. Threatened to knock the MD out cold and even shoved him out my way when he tried to stop me leaving. Despite the aggression on my part the CAB said they had no right to do this and literally 1 day before I was due to start proceedings against them after sending them a strongly worded letter the cheque arrived in the post.