Use of the word “best” and other superlatives needs particular care.
If the superlative is subjective, cannot be measured and is presented clearly as a matter of opinion, the claim does not need substantiation, e.g. “it’s the best holiday ever/I had the best holiday ever”.
If the superlative is objective, can be measured against factual criteria and is presented as fact, the claim needs to be supported by satisfactory evidence, e.g. “the UK’s largest X company” or “X’s favourite xxx”.
As well as supporting evidence, objective “best” claims may need to be qualified in the copy, e.g. “with over 24,000 square feet of floor space, we’re the best furniture retailer in the North West”; this makes clear that “best” relates specifically to size rather than, for example, sales.
Claims such as “the UK’s number one/premier/favourite X company” and “Britain’s leading Y specialist” are seen as factual claims which imply market leadership. Satisfactory evidence is needed, e.g. volume of sales and market share and turnover compared with other competitors.
“Top parity” claims state or imply that the advertiser or their products are amongst the top of the range, but are not above the rest. Top parity claims are acceptable (e.g. “nothing acts faster”) with satisfactory substantiation that the product performs as well as its leading competitors. Radiocentre cannot clear superiority claims based on top parity evidence, i.e. “biggest range” where competitors offer a range of the same size.