I'll give you that Chiltern Railways revenue protection have better things to do than meet this bus to check tickets.
I guess that also a replacement bus is also not registered with the Traffic Commissioner, so can't be regarded as a stage carriage bus, but in the overall context of railway revenue, taking a bus for free because of gaps in railway bylaws is not consistent with the principle of honesty about paying for the railway's provision of a service. If the public aren't required to pay for a replacement service, why is the railway required to provide one?
The public are prepared to pay for one, but there is no mechanism to do so. If you want to leave the bus’ route to approximate the fare yourself by touching in at rail stations that’s up to you. But nobody pays for the bus, and the drivers confirm it’s free.
Chiltern could actually set up the bus to demand payment of the due contactless fare, quite easily. There is only one fare that can be charged. But, they don’t. That’s up to them I guess. That’s why this particular bus, is, as the thread title asks, *actually free*.
The railway is required to provide the bus because it is avoiding the expense and hassle of a withdrawal process, not because the bus is in any way useful to passengers. It is used exclusively by cranks - for free.