What is the maximum number of people on a guided tour

Typically, the group size is about 6-8 people. We can accommodate 9 people normally, though for some special groups (e.g. a club booking) we can accommodate more. Once we can no longer seat people in the 10 seater mini coach the tour is closed off (we often go out to dinner in the coach in the evenings, or maybe drive to a difficult-to-get-to-by-bike scenic viewpoint.)