Right guys,
I sent all 6 injectors off to be tested, low and behold, injector 3 has zero flow on idle. Got it rebuild, fitted it this evening, and I've got a smooth idle! Took it for a drive, no fault codes and no lights. Low rail pressure seems to have disappeared now too.
Just want to say a massive thank you to everyone that gave advise. I can finally get back to work now 😂!
Cheers once again!