Many thanks for all the suggestions.
In the old days I could have walked around to my friends house, nowadays the best we can get is skype. Pictures are never quite enough and can never beat actually being on the ground.
Anyway, I suggested he re-pot into a soil mix that is suitable for cannabis which he did pretty much straight away. This morning he emailed to say everything already looks a lot better.
I will try and get a few images later in the week and share the progress with you.
Hopefully it is a problem solved.
Many thanks,
TF