Note: This advice is given by the CAP Executive about non-broadcast advertising. It does not constitute legal advice. It does not bind CAP, CAP advisory panels or the Advertising Standards Authority.

“Leading” claims are likely to be interpreted to mean best-selling, unless the ad makes an alternative meaning clear. These claims are likely to be considered objective comparisons

The CAP Code requires advertisers to hold documentary evidence to substantiate claims that consumers are likely to regard as objective and that are capable of objective substantiation. Additionally, any comparisons with identifiable competitors must be verifiable and comply with other relevant comparisons rules (3.33 – 3.40). See also Comparisons: Identifiable competitorsTypes of Claims: “Best-selling” and Comparisons: General



Is sales data always required?

Alternative meanings


The CAP Code requires advertisers to hold documentary evidence to substantiate claims that consumers are likely to regard as objective and that are capable of objective substantiation.

The nature of the evidence required to substantiate “leading” claims will vary depending on the context in which the claim is made and how it is likely to be understood by its audience. However, when making unqualified “leading” claims, it is likely that these will be understood as best-selling claims, and comparative evidence relating to unit-sales, market share, or both, will be required. Self-reported consumer data or third-party awards will not be sufficient to support a claim that would otherwise require objective substantiation.

Absolute “leading” claims are likely to be understood to be an entire market comparisons, and marketers would need to be able demonstrate that they are the best-selling across the entire market, taking into account all competitors. In 2018 the ASA upheld a complaint about the claim “the UK’s leading trade mark advice and registration company” and “The no.1 firm in the UK”, because the data used to calculate the number of trade marks registered by the advertiser and its competitors did not include many competitors who may have registered a similar number or more (Trade Mark Direct Ltd, 11 April 2018). 

Marketers must consider how consumers are likely to interpret any leading claims made, and hold evidence to support that likely interpretation. The ASA considered that, in the absence of any qualification, consumers were likely to understand the claim “THE UK'S LEADING PROFESSIONAL ORGANISATION FOR INTERIOR DESIGNERS” to mean that, relative to other organisations in the field of interior design, the advertiser had the highest total number of members. Because it had only provided evidence that compared its size with one other organisation, and had excluded other interior design organisations on the basis that they had not listed their members or specified a length of term of directors, the evidence did not substantiate the claim (British Institute of Interior Design, 18 December 2019).

The ASA ruled against an ad which stated “the leading home show brand in the UK”, because, whilst the advertisers had evidence relating to the total number of people involved in the show, including staff and exhibitors, the ASA considered that the claim would be interpreted to mean this show had the highest attendance rate of consumers compared to competing events (Media 10 Ltd, 30 August 2017).


Marketing communications do not need to explicitly identify the competitor or product being compared to be subject to the rules on comparisons with 'identifiable' competitors. If a consumer can identify at least one competitor or competing product, whether or not it is identified explicitly in the ad, rules 3.33 – 3.37 will apply. In most cases, “leading” claims are likely to be understood as comparisons with identifiable competitors. This type of comparison is allowed as long as claims are based on objective criteria and are presented in a way that is unlikely to mislead. See Comparisons: identifiable competitors.

The CAP Code requires that comparisons with identifiable competitor products “must objectively compare one or more material, relevant, verifiable and representative feature of those products” (rule 3.35).

The information required to make a claim verifiable will depend entirely on the specific comparison and the evidence used to support it. Generally speaking, marketers should include, or direct consumers to, sufficient objective information and data to ensure that consumers are able to check the claims are accurate for themselves (see Vodafone Ltd, 28 July 2021). If verifying the comparison requires specialist knowledge, consumers should be able to get a knowledgeable and independent person or organisation to verify the comparison for them.

The ASA considered that consumers would understand the claim “Industry Leading Performance and Reliability” to mean that the products provided by Trappex had superior performance and were more reliable than comparable products provided by their competitors. They also considered that consumers interested in Trappex’s products would have sufficient knowledge of the market to be able to identify at least one of Trappex’s competitors, and therefore, this was a comparison with identifiable competitors. Because Trappex they did not provide any evidence to substantiate their claims, or include any information, or direct consumers to an alternative source of information, to ensure the details of the comparison could be verified by consumers and competitors, the ad breached the Code. (Trappex Ltd, 18 August 2021).

For detailed advice on this requirement, see Comparisons: Verifiability.

Is sales data always required?

Whilst in most cases a “leading” claim will be a best-selling claim that needs to be supported by sales data, in some circumstances, advertisers may be able to substantiate a “leading " claim without holding evidence relating to their competitors’ sales.

The ASA accepted data collated by an independent third party over a six-month period which compared an advertiser’s web traffic with that of its competitors. The results showed that the number of unique visitors was more than its four closest competitors combined and more than double the number of total visits than its closest competitor. The ASA considered that, while visitor numbers alone was generally not a guaranteed indication of market share, because the difference in web traffic was so great, in these particular circumstances, it was reasonable to infer that the advertiser was the leading provider and had substantiated the claim ( Ltd, 14 February 2018).

Alternative meanings

CAP recommends that marketers exercise caution when using “leading” to denote anything other than “best-selling” and ensure that any other intended meaning is both clear and supportable.

If an advertiser intends to use “leading” to mean something other than best-selling, the ad should make this explicitly clear, and the advertiser should have evidence to support that claim. The ASA considered that consumers would understand the claim “Why AnyJunk? … Industry leading green creds” to be an objective claim that AnyJunk was ranked the highest in terms of being environmentally friendly compared to all other rubbish removal companies, rather than a best-selling claim. Because the advertiser could not provide comparative evidence which demonstrated that it was more environmentally friendly than any other major waste management company, the claim was misleading (Anyjunk Ltd, 30May 2018).

In 2012, the ASA upheld complaints about a claim that a model engineering show was “the leading show of its kind”. Although the advertiser argued that the claim had been based on the number, content and variety of exhibits, the ASA considered that this would be understood to relate to visitor numbers, and the advertiser did not have evidence to substantiate the claim (Meridienne Exhibitions Ltd, January 2012).

Marketers may sometimes intend a “leading” claim to mean “first to the market” or “innovative”. For the ASA to accept that interpretation of the claim, marketers would need to have made it clear that a best-selling statement was not intended. In 2014, the ASA held that, in the absence of a clear indication that the intended comparison was between the technology and degree of innovation involved in the advertiser’s product and those of its competitors’, the claim “the leading manufacturer of downdraught filter bench technology” would be regarded as a claim that the advertiser had the greatest share of the market (Air Cleaning Systems Ltd, February 2014). However, in 2013, the ASA accepted that the claim “world-leading technology”, which appeared alongside the claim “innovative solutions”, was likely to be understood by consumers as referring to the inventive nature of the product, rather than as a comparative claim regarding the advertiser’s market share (Eco Solutions, October 2013).

Whilst there may be situations in which the ASA would interpret a “leading” claim as being the subjective opinion of the advertiser, if the claim is clearly intended to refer to a subjective matter of opinion, in practice such claims will almost always be regarded as objective. See Types of claims: puffery and Matters of opinion

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