There's some data here from the ONS:
https://www.ons.gov.uk/visualisations/dvc363/babyindex.html#0,Nicholas
According to the ONS, Nicholas was a vey popular name from the 1950s until the 1990s but after about 2003 it just dropped off the list altogether.
As I mentioned above, my DB did sometimes have people call him names but I guess that everybody gets that to some extent.
I have known a couple of Nicholas's in addition to my brother and they all, without fail, went by the name of Nick, even in professional situations. The only time I ever saw then use "Nicholas" was on official forms eg driving licence or passport or job applications etc.
I also remember that our mum always used to call him by his full name when he was in trouble!
"Especially because it needs to vaguely work in Greek as have family in Cyprus."
I would guess even here the family would likely use whatever is the Greek diminutive for Nicholas.
My DH was born abroad and his name is Nikolai. He always gets called by the diminutive for that in his own language.
So, I guess what I'm trying to say is that if you do then he will most likely be known as Nick or some other similar diminutive and he will likely associate his full name with being in trouble. eg if you ever shout out something like "Nicholas [middle name] Geueiiii, you get here right now!"