The maximum isn't five, a site near us has nine. It is not correct that planning isn't needed, it is just that a different system exists between the Caravan Club, The Camping and Caravan Club and planning. The applications are all lodged with planning via the clubs and dealt with in house rather than going out to consultation. A planning notice goes up. Our Parish Council objected to a proposed site on access grounds and it was withdrawn. The sites are looked at quite carefully by the clubs and not all are even put through if there are issues.
Anyone staying at the CC or C&C site are supposed to be members of the club.
Under the 28 day rule you can have as many caravans as you want, our local school does this on their playing fields, weekends and school holidays but they have to be there for a common event such as a club rally, a fund raiser, scouts weekend etc.