Agree with those draft reps. Having checked google street view again and spotted red signs at the entrance stating "No access for unauthorised persons", I'd be tempted to embellish a little as follows (have also added an optional additional paragraph).
I make representations against PCN number xxxxxxxxx on the basis that
The contravention did not occur
Schedule 9:7:6 of the TSRGD 2016 defines a box junction as follows:
"For the purposes of this paragraph “box junction” means an area of the carriageway where the marking has been placed and which is—
(a)at a junction between two or more roads;
(b)at a gyratory system or roundabout;
(c)along a length of a two-way road (other than at a junction), the carriageway of which is not greater than 4.5 metres wide at its narrowest point; or
(d)on the length of road adjacent to the vehicular entrance to the premises of a fire, police or ambulance station."
The RTRA 1984 at s192 describes a road as:
F13 road”—
(a)in England and Wales, means any length of highway or of any other road to which the public has access, and includes bridges over which a road passes, and
(b)in Scotland, has the same meaning as in the Roads (Scotland) Act 1984;
Whilst Ley Street is a road within the definition, the placement of the box junction markings on Ley Street is at the driveway entry to a Council depot, a place the public do not have access by right. Indeed, there are signs placed at the entrance to the depot explicitly saying "No access for unauthorised persons".
It follows that the box junction markings are laid outwith the parameters set by law and no penalty can be enforced.
Further to this point, I note the PCN issued by the authority states the location of the alleged offence as Ley Street (only). Given Ley Street is a long road which has more than one box junction marked along it, the PCN must be more specific as to which box junction it is referring to by distinguishing which road it is a junction with (it is a strict requirement of the relevant legislation that a PCN must state the grounds on which the authority believe a penalty is payable and leaving the location ambiguous is not consistent with this requirement). The fact the box junction marking is not actually placed at a junction with a second road presumably prevents the authority from doing this at this location.