https://www.gov.uk/government/publications/urgent-safety-advice-012023-passenger-doors-not-centrally-controlled-andor-locked-by-train-crew/urgent-safety-advice-012023-passenger-doors-not-centrally-controlled-andor-locked-by-train-crew

Heritage railways and other operators of trains who use passenger coaching
stock without doors which are centrally controlled and/or locked by train
crew (principally slam door rolling stock) should review the risks
associated with the use of train formations which may not be fully
platformed or which are of a length close to that of the platforms being
called at.

Duty holders should ensure that a suitable and sufficient assessment of the
risks is carried out and that any appropriate control measures identified
are implemented. These assessments should consider:

the type and location of passenger doors on the relevant rolling stock
the length of passenger trains compared to the platforms at which they may
call
the capabilities of the braking systems of the trains involved and the
level of precision which is reasonably achievable by them when stopping
the level of accuracy in stopping position required of train crew and if
this is supported by relevant competency and assessment processes
if the level of stopping position accuracy required of train crew aligns
with the capability of the trains involved and the accuracy required at the
relevant platforms
the effectiveness of existing measures intended to manage the risk of
passengers exiting a train that is not fully platformed or which may stop
in line with areas not intended for public use, such as platform ramps
the visibility from the cab of different traction units and the
effectiveness of any stopping markers in place.