I'm getting fairly sick of having to keep repeating this ...
BS 1362 establishes a minimum standard but, provided that is satisfied, the 'rating' depends on the actual product, and is indicated in manufacturer's Specification.
BS 1363 requires that a double socket passes the temperature-rise test with a total current of 20A (14A + 6A), but that in no way means that a company cannot manufacture (let alone 'is prohibited from manufacturing'!) a product which passes that test at 26A (so obviously still BS 1363-complaint) and hence in the Specification indicate that the 'rating' of their product is 26A.