Caravanning and camping with a dog is a well-established part of British holiday culture, and the large membership organisations behind it — the Camping and Caravanning Club and the Caravan and Motorhome Club chief among them — run extensive networks of sites that welcome pets as standard rather than as an exception.
The near-universal rule across sites is that dogs stay on a lead within the site itself, even where they might be allowed off-lead on nearby open land, simply because of the density of other pitches, children and shared facilities. Most sites cap the number of dogs per pitch, commonly at two, and expect waste to be cleaned up immediately using the site's own disposal points.
Beyond the membership-club networks, independently run campsites and small farm-based sites are similarly often dog-friendly, and tend to have the most relaxed, walk-straight-from-your-pitch access to surrounding countryside — a genuine advantage over a hotel stay if hiking or walking is the main point of the trip.