national insurance/working hours

[firewatch]

I have a 15 year old brother in law who is on work experience cooking at a local hotel, they really like him and want to give him more hours but would like to pay him.
He does not have a national insurance number, and is unsure of the hours he could legally work.
Is there anything or anyone who knows of the laws etc surrounding this issue??We are at a loss and his mum really wants to know before allowing him to do any more than his work experience.

[Tom Braider]

See this link

http://www.direct.gov.uk/en/YoungPeople/Workan dcareers/Yourrightsandresponsibilitiesatwork/D G_066272