For Control Periods 4 and 5 the Schedule 4 Restrictions of Use regime included ‘cover’ for bus costs (as well as revenue loss) and the structure of Access Charge Supplements reflected this. The TOCs are ‘held harmless’ by the DfT (or equivalent franchising or concessioning body) to financial changes at a Periodic Review. Obviously assumptions are made about future bus costs, no doubt based heavily on previous experience. Thus the TOCs have had relatively low risk in this area.
I have been retired too long to know whether a similar arrangement has been applied for Control Period 6 but would be surprised if it hadn’t been.
The situation would now appear to be that RRB costs are likely to rise significantly because of changes in legal understanding since the Periodic Review 2018, carried out with the full involvement of public bodies, notably ORR, DfT and Network Rail. I can understand why thinly capitalised TOCs are uneasy that they have to take all the ‘hit’ if they had been planning more or less on business as usual.