That's not lawful and on the face of it is a clear procedural impropriety.
From the General Regs
Notice to owner
20.(1) Where
(a)a penalty charge notice has been given with respect to a vehicle under regulation 9, and
(b)the period of 28 days specified in the penalty charge notice as the period within which the penalty charge is to be paid has expired without that charge being paid,
the enforcement authority concerned may serve a notice (a notice to owner) on the person who appears to it to have been the owner of the vehicle when the alleged contravention occurred.
From the Traffic Management Act:
owner, in relation to a vehicle, means the person by whom the vehicle is kept, which in the case of a vehicle registered under the Vehicle Excise and Registration Act 1994 (c. 22) is presumed (unless the contrary is proved) to be the person in whose name the vehicle is registered;
