After GNER lost a court case relating to Grand Central, in about 2006, the then Rail Regulator, Tom Winsor, wrote an article which claimed that it was not necessary to hold a franchise in order to run an passenger rail service. Theoretically, that's true, but there are not many routes on which it is likely to be profitable to run an Open Access service, and you have to satisfy the ORR that your proposals are not primarily abstractive of existing franchised operators' revenue, which further limits the opportunities. Finding available paths is another difficulty.
It's not just theoretically true, it's factually true.
Stagecoach were the first Open Access operator when they hooked a couple of their own carriages to the overnight sleeper and sold tickets for those carriages themselves. No extra paths required, no separate locomotive required, no franchise.
There is absolutely no technical reason why they couldn't, for example, refurbish a half a dozen Mk3 coaches and pay Scotrail to add one to 6 7-City sets and haul them around as "Scottish Megatrain" coaches.
Likewise. If Stagecoach were to lease a 5-car IEP unit and run it from Perth via Stirling to Edinburgh at 7am, then hook it up to the back of a 5-car LNER service on the way to London. It's only one path leaving Edinburgh and one driver.
Obviously it takes "two to tango", but at the back of my mind I'm wondering if ancient legislation compels a rail operator to interline goods wagons and passenger vehicles...
