Clamping is not a penalty, so costs can be charged.
Railway Byelaws 2005
14. Traffic signs, causing obstructions and parking
(1) No person in charge of any motor vehicle, bicycle or other conveyance shall use it on any part of the railway in contravention of any traffic sign.
(2) No person in charge of any motor vehicle, bicycle or other conveyance shall leave or place it on any part of the railway:
(i) in any manner or place where it may cause an
obstruction or hindrance to an Operator or any person using the railway; or
(ii) otherwise than in accordance with any instructions issued by or on behalf of an Operator or an authorised person.
(3) No person in charge of any motor vehicle, bicycle or other conveyance shall park it on any part of the railway where charges are made for parking by an Operator or an authorised person without paying the appropriate charge at the appropriate time in accordance with instructions given by an Operator or an authorised person at that place.
(4) In England and Wales
The owner of any motor vehicle, bicycle or other conveyance used, left or placed in breach of Byelaw 14(1) to 14(3) may be liable to pay a penalty as displayed in that area.
(ii) Without prejudice to Byelaw 14(4)(i), any motor vehicle, bicycle or other conveyance used, left or placed in breach of Byelaw 14(1) to 14(3) may be clamped, removed, and stored, by or under the direction of an Operator or authorised person.
(iii) The owner of the motor vehicle, bicycle or other conveyance shall be liable to an Operator or an authorised person for the costs incurred in clamping, removing and storing it provided that there is in that area a notice advising that any vehicle parked contrary to these Byelaws may be clamped, removed and stored by an Operator or an authorised person and that
(i) the costs incurred by an Operator or an authorised person for this may be recovered from the vehicle’s owner.
(iv) The power of clamping and removal provided in Byelaw 14(4)(ii) above shall not be exercisable in any area where passenger parking is permitted unless there is on display in that area a notice advising that any vehicle parked contrary to these Byelaws may be clamped and/or removed by an Operator or an authorised person.
24. Enforcement
(1) Offence and level of fines
Any person who breaches any of these Byelaws commits an offence and, with the exception of Byelaw 17, may be liable for each such offence to a penalty not exceeding level 3 on the standard scale.
(4) Notices
No person shall be subject to any penalty for breach of any of the Byelaws by disobeying a notice unless it is proved to the satisfaction of the Court before whom the complaint is laid that the notice referred to in the particular Byelaw was displayed.