When you talk about Permits to Fly you need to be specific about the category of aircraft you are looking at, eg PFA, BMAA and ex-military under or over 2730kg. Each has its own slight differences.
For example some have to be maintained by CAA approved companies (ex-mil over 2730kg) whilst others by a person acceptable to the CAA.
Md600 driver - there is an AIC issued that allows some types of paid training in ex-military aircraft. The CAA recognised the need for proper training and issued an AIC to allow training in the jets but has recently extended this to include the ex-mil helicopters. Unfortunatly, it does not include the gazelle, as I understand training can be obtained on certified models, but it will help the Scout boys keep legal.
Max/Min occupants - You need to read the actual aircraft's Permit to Fly. Most state the max number of occupants and the min crew for display flying. For some ex-mil types with more than two seats the wording is slightly different and allows the carraige of crew, which I think is defined as flight crew plus engineers for the operation of the aircraft away from base! pax!
ACX