Contracts like this can be very lucrative, you don't have to sell any tickets, you get paid if the aircraft is full or empty. So anyone bidding to take it over will have factored in the cost of any tupe implications, obtaining extra aircraft etc. Small change really over the life of a 3 or 5 year contract. In situations where tupe applies, but is ignored then you are basically in an employment tribunal dealing with cases of unfair dismissal.
If a Filton to Tolouse service is also included, then more crew will be required to run it than the current Chester-Filton route. Contracts like this are normally quite strict about level of service etc, so a spare aircraft or good engineering cover may have to be in place
Suspect it will end up with a couple of extra aircraft being leased in, some tupe crew from eastern coming across, some seconded crews from other bmir bases, and possibly over time bmir establishing a perm base at one of the locations involved?