I think it sounds like time he sat down and renegotiated his salary. If they need him to increase his hours and shoulder more responsibility than they have previously - a sudden and constant increase in his hours to save them the money it would cost them to employ the extra chef they obviously need - then I would be suggesting that he discusses the issue with his Head and the owner.

ETA: Do any of these extra hours go to time in lieu?
he had a meeting with the powers to be last week where they talked about a pay rise. who knows if they will come through with that one. They have an ad running at the moment to fill a position, but they arent getting any bites that the powers to be like (wrong age, not enough experience etc)
Nah no overtime goes to time in lieu, that only happens for public holidays.

He isnt on the award, but if he pushed to get the award wage, then the base wage would be smaller but then he would have to be paid for every hour over the 7.6. So if they were to adhere to that then it would be worth while.