But surely this can only be in the margins, or else an unsuccessful bidder could cry 'foul'.
Who is going to cry 'foul'? We are talking several years into the contract of a tendered bus service and all operators want to benefit from council flexibility so you would have to be a grade 'A' idiot to kick up a fuss over an operator getting the same treatment you are asking for and these sort of negotiations and matters are less publicly known.
It will be harder for this to happen under franchising as everything is more rigid and contractual so if the operator doesn't get their pricing right and the authority don't get their price review (inflationary increases) right then that is where the friction will kick in.
I've not seen contracts like that. Those in London were typically 5 +2 year contracts, so presumably there is no penalty for terminating at 5 years. And what happens if the contracted is terminated after 3 years because the contractor has gone bust - there would be no money to pay such penalties.
If there are penalties for early termination for contractors, are there penalties on the commissioner for terminating contracts early as well? For example, if the route is cut back, hours of operation reduced etc?
But I suspect we are beginning to drift off topic.......
They aren't common in the bus industry with normal tendering, though I do know one of the Combined Authorities had a contractual term requiring an operator to pay the difference between their price and the replacement operator for the term of the original, contract if they handed it back and a shire county who had a term that meant if you handed back a contract early you were removed from the tender list. Whilst never explicitly stated by either party it is suspected that a punitive contract guarantee against the owning group was why Stagecoach pulled out of Dumfries & Galloway given what they said.
They are more common with larger outsourcing contracts, which bus 'franchising' comes under and all the rail franchises had such guarantees (and the guarantees/penalties are with the owning group not the operating subsidiary so a big group making their subsidiary go bust won't get them out of it) to stop businesses trying to wriggle out of a poorly performing contract.
As my dad, who used to work in IT procurement as a consultant, says "the profit is in the variance". Depending on how well written was the original contract the variation may well be where contracts are rescued, either marking up enhancements above actual cost or not passing on all savings of reductions, but it does depend on how well written the contracts were (and UK government at all levels does appear to be particularly bad at writing these sort of things in general). Even with normal bus contracts there are notice periods that have to be adhered to (often related to registration notice periods for instance) and a council would be as tied to them as the operator is - as with many of these things in the deregulated market with normal route tenders there may be flexibility from both sides (we'll forgo some of the notice on ending now because you were flexible earlier) assuming the relationship is good but that is less available in the more formal and contractual franchise system.