There is a flaw in the system though - the Marston Vale line. We have no ticket machines ( thus no pf) and guards often unable to sell. I have been pulled up many a time at Euston for no ticket and had to argue my way out of things
It would be advisable to buy a ticket when changing at Bletchley.
That would, at the time of the main London commuter connection, involve missing the train.
A TVM on platform 5 or 6 would help, though.
As long as it had 'tickets from another station' enabled.
I have been pulled up many a time at Euston for no ticket and had to argue my way out of things
That's where I've had issues too. Apsley station ticket office has (had?) one permanent member of staff, so when they were ill/on holiday it didn't open. The TVM didn't accept cash. The hassle I sometimes got at Euston was really something I could do without. Even getting it in writing from LM that I can board without a ticket if I'm paying cash/voucher didn't massively help.
Barrier staff rather than RPIs, admittedly, but still.
Apsley station ticket office has (had?) one permanent member of staff.
Two regulars nowadays, swapping morning and afternoon shifts.
Always found them helpful and friendly.