If you believe the customer needs to be able to demand a better class of bus driver Geoffers, the bus trade association and/or the bus drivers themselves have to do the spadework of defining superior competence; I don’t think you can expect those outside the trade to understand the detail.
Customers would then have options at tender time – say P1s with:
Level 1: 6-monthly and annual checks as now.
Level 2: gets four hours sim above the minima every year
Level 3: 1 + 2 + an extra annual line check with another company’s examiner
These are only examples, may be unworkable, don’t actually enhance competence, only exposure to more training, and will have a cost, but at least the customer would have different “pilot competence” options and prices when picking his supplier. Should he then face a duty of care action, his face may be red if he asked for Level 1 pilots instead of something better. After that, changes might follow.
Of course a single bus company may decide there is benefit in starting down this track unilaterally; I hope they do and that they profit from it; it’s commercially risky but if it succeeded, others would be dragged along in their wake.
But then I have to repeat that this would not directly increase competence, only the costs and the numbers of training hours; we have to define the trainable aspects of superior pilot competence before we can hope to develop it.