Regs aren’t retrospective, if it’s a new installation then yes needs SPD, as you are carrying out an Eicr I would code it C3 and leave it to the client to decide.

Lol. Like the clients an expert. 

What data is available to advocate spd's

Answer.. none.

Just engineering mumbo jumbo from so called experts offering no statistical observed empirical data.

Bit like climate change but I didn't say that.

Careful reading of Chapter 65 might lead one to conclude that there is no requirement to consider recommendation for improvement. Unless the issue would give rise to danger, there is no requirement to mention it and therefore a Code 3 could be dispensed with. 
I wonder if I just stuck an appendix in at the back of my reports listing out some of the common code 3 issues and directed the client’s attention to it, or, perhaps, just inserted a link to Best Practice Guide 4……mmm, ….always the rebel, or so my headmaster told my parents!
Then again, my dad’s warning that rebels usually find their way to the gallows is still worth heeding!

Careful reading of Chapter 65 might lead one to conclude that there is no requirement to consider recommendation for improvement. Unless the issue would give rise to danger, there is no requirement to mention it and therefore a Code 3 could be dispensed with. 
I wonder if I just stuck an appendix in at the back of my reports listing out some of the common code 3 issues and directed the client’s attention to it, or, perhaps, just inserted a link to Best Practice Guide 4……mmm, ….always the rebel, or so my headmaster told my parents!
Then again, my dad’s warning that rebels usually find their way to the gallows is still worth heeding!