Hello Diane,
The National Caravan Council, are the guardians of safety and construction for the sale of caravans in the UK, and only if the caravan meets the relevant regulations and standards with the NCC issue a certificate of conformance denoted by the NCC badge on a caravan.
"BS EN 1647:2004
Leisure accommodation vehicles. Caravan holiday homes. Habitation requirements relating to health and safety" - includes references to thermal insulation for mobile homes, and touring caravans. But be warned that simply reading such standards can be confusing, a manufacture can often exclude or modify the particular clause, by special claims or limitations of the scope of use.
For example a manufacture may state that a particular model is not designed for use in winter, or not for continental use, which may allow for a lower standard of insulation.
To make sense of such standards you must have all the relevant product specification information, which some manufactures will consider is commercially sensitive. And thus will be reluctant or even refuse to disclose.