I will leave the rail ticketing angles of this to those who understand it better than I do.
What I would question is the (coach) drivers' hours and employment law angles of it.
From the employment law angle first, I would say that the travelling time (be that on train, or as a passenger in the coach they drive some of the time) would count as working hours, and therefore ought to be paid. If any of this time being unpaid puts the drivers below the legal minimum wage, they would have a case for minimum wage breach.
Also, I can't help thinking such time spent doing something because the employer wants them to (i.e. travelling) would count as part of working day for drivers hours rules. I'm inclined to think that, because they are doing what they have been told, rather than spending the time doing what they want, it would be dubious to class it as 'break' for drivers hours rules - I'd be inclined to say it's 'other work'.
I'm not entirely expert in tachograph related stuff (what PSV driving I do is 'domestic hours') but I'm aware there have been test cases involving drivers being required either to drive or travel passenger in a car to get from operating base to wherever they are taking over their coach, and what this time counts as for drivers hours purposes.
And bear in mind that both the operators' O-licence and the drivers' PCV licence/s are at risk for breaches of drivers hours.
(The above subject to the disclaimer that I'm not a lawyer or police / VOSA officer)