So how do the private security 'officers' that staff major InterCity stations fit into this? Are they authorised to act as an "Authorised Person" under Byelaws and NRCoC▸ for all TOCs▸ etc?
They can indeed be authorised by an Operator to enforce the Byelaws. (NRCoC is irrelevant by the way.)
Reason I ask this is for the reason that you cannot be Penalty Fared by London Midland staff at London Euston if you've used a Virgin Trains service. Does the same apply here in respect of the byelaws? i.e. GreaterAnglia private security yet using a London Overground section of a station?
Take Euston for example. The moment you step off a London Overground train and on to a platform you are covered by the National Rail Byelaws. That's because it isn't a
TfL» premises. The Underground on the other hand, is. I believe that Network Rail security work for STM. STM are also a contractor for London Overground security, you may find that in some instances a company may be authorised to enforce both sets of Byelaws.
The National Rail Byelaws and Transport for London Byelaws are broadly similar anyway, except that the TfL ones have more explicit references about alcohol possession and the TfL Byelaws can additionally be enforced by Home Office PSCOs.
Say for example, at Birmingham New Street, a London Midland member of staff could enforce a Byelaw on an
ATW▸ train, a Virgin member of staff could enforce a Byelaw on a CrossCountry train and so on without any issue as they all come under the same National Rail Byelaw umbrella.
Finally, Rail Replacement Bus Services............ Presumably the Bus/Coach Driver is an "Authorised Person" and if you "disobey" the request you could find yourself in trouble?
The Byelaws do not apply to rail replacement bus services.
That's because a bus isn't a "railway asset". This is defined as:
(a) train;
(b) network;
(c) station;
(d) light maintenance depot;
and any associated track, buildings and equipment;