my static caravan is wired in t&e some of the downlights are wired in flex, know this because changed a 3gang to 6gang switch and a few flexes were present all perm lives are t&e. Even have a 25A RFC lol although on a 16A hook up.I would say mobile cabins ie portacabin style site offices etc are regular twin and earth, as are static caravans.
They are transportable, rather than towable.
The 230V side of a touring caravan that gets pulled up and down a motorway at 70mm is wired in flex.
Reply to the thread, titled "Mobile cabins cable type" which is posted in UK Electrical Forum on Electricians Forums.