Back here in the U.S., Park Model homes have a slightly different description than, apparently those in the U.K., so use caution.
Park homes here are not neccessarily mobil homes that have been moved onto a fixed location permanently. Park homes can be constructed as usual or they can be "modular homes"... those bult to strict standards but in "modules" that can be moved and then put together at the homesite.
The concept of "Park Homes" was actually began by Mr. Art Linkletter, an early TV and radio personality back in the 1950's or so. He (and other investors) started contructing very nice (but small) home sites in the Phoenix, AZ arprimarily for retirees. The earlier "Parks" consisted of winding streeets with attractive but desert type landscaping. Since the only less expensive homes of the times were trailer houses (as their known here) of various lengths... sometimes up to 60 feet or so. As time went on more of these popular retirement parks were constructed especially with the advent of the previously referenced modular homes.
Some cities, especailly in Arizona are almost exclusively Park Homes... such as Sun City and others...