I would have thought that a franchisee can employ as many people as he wishes, you should encourage it, the bigger he gets the more you get.
I think it's highlighted a problem at £8 p/h and your 15% the work is either not of sufficient value or your franchisee is not quick enough an employee should be around 25to 30% cost of the turnover so with your 15% that leaves the franchisee 55% - is that enough, probably not.
That's where your cut will stunt the growth of a franchise , alternately make him a second franchise where he sends an employee out on his own.
Darran