Peter Goodland wrote:

Of course this wouldn't work here on trains with DOO

It does in Germany, where rural trains are often DOO. You're meant to
be able to buy a ticket off the driver, but they usually don't carry
money or a machine, so you just go and tell him, and he tells you to
sit down and that he'll inform any inspectors that board. This
normally means a free journey.

That said, I can't see the cab door being left open working on services
out of London...

Neil