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.

The likely interpretation of a “number 1” claim will depend on the product or service advertised and the context in which the claim appears. Marketers intending to make a “number 1” claim should consider how consumers are likely to interpret the claim in the context of the ad. Unless the claim is likely to be understood to have another meaning in the context of the ad, or the meaning is ambiguous, the ASA is likely to regard “number 1” claims in the same way as “best-selling” or “leading” claims.

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

How will consumers interpret the claim?



Is sales data always required?

How will consumers interpret the claim?

There may be situations in which the ASA would interpret a “number 1” claim as being an obvious exaggeration (puffery), or a claim which is unlikely to be taken literally (Code rule 3.2). See Types of claims: puffery. In practice however, “number 1” claims will almost always be regarded as objective comparisons. Marketing communications must make the meaning of the claim clear. 

The ASA has considered multiple unqualified “number 1” claims, when made in reference to a product or service, to mean that the product/service has the largest market share. For example “#1 World’s Live-Games Provider” (ASTOK Ltd, 15 April 2020) "EUROPE's NO.1 AIRLINE" (Ryanair Ltd, 07 February 2019), “the UKs [sic] No.1” (Skinny Tan, 18 October 2017) and “The UK’s number 1 breakdown service provider” (AA Ltd, 20 July 2022).

Some “number 1” claims are likely to have an alternative meaning to consumers, because of the context in which they appear, or because they are qualified. For example “BOXT are also rated Britain’s number one heating company on Trustpilot”  (BOXT Ltd, 15 July 2020) and “Our Arts and Humanities research is number 1 in the UK for overall research quality (GPA) in #REF2021”  (The University of Leicester, 07 September 2022). The ASA considered that consumers would understand that the claim “the UK’s best mobile data network”, alongside the claim “No. 1 Mobile Network Performance. nPerf. 2019” was based on the results of mobile data network testing undertaken by nPerf, rather than a best-selling claim. (Vodafone Ltd, 28 July 2021).

Some “number 1” claims may have multiple possible interpretations, and the meaning will be considered ambiguous. The ASA considered that the claim “Unlimited data, now available on the UK’s No.1 network” would have had a number of different possible consumer interpretations, including as a comparison using objective measures such as highest turnover amongst mobile providers, having the most customers, or offering the best-selling product/package (EE Ltd, 08 April 2020). See also Telefonica UK Ltd, 24 February 2021. The claim "Derby's No.1 Award Winning Agent" was also considered ambiguous because it could have been understood to mean that the agency had won the largest number of awards compared to other agents in Derby, or that that it had won at least one award and also had let the most properties (IMS Lettings Ltd, 17 April 2013). See also (Agency Management Ltd, 07 November 2018).

Marketing communications which do not make the basis of the claim clear are likely to be considered misleading, and marketing communications must make the meaning of the claim clear.


The CAP Code requires marketers to hold documentary evidence to substantiate claims that consumers are likely to regard as objective and that are capable of objective substantiation (3.7).

The nature of the evidence required to substantiate “number 1” claims will vary depending on the context in which it is made and how it is likely to be understood by its audience.

When making best-selling “number 1” claims, it is likely that comparative evidence relating to unit-sales, market share, or both, will be required. Absolute “number 1” claims are likely to be understood to be entire market comparisons. To make this type of claim marketers would need to be able to demonstrate that their product or service is the best-selling across the entire market, taking into account all competitors or competitor products/services.

The ASA upheld a complaint about the claim “#1 holiday website on the planet”, because the advertiser did not provide evidence to demonstrate that the advertiser had the largest turnover of holiday rentals when compared to its global competitors (Rental Republic Ltd, 19 January 2022). Similarly, the claim “the UK’s No.1 Trade Mark Service” was not adequately substantiated because the data did not include details about the number of trade marks registered by many of the advertiser’s competitors, which may have registered more (Trade Mark Direct Ltd, 11 April 2018).  

Marketers must ensure that the way data is collected for their own sales and competitor sales is sufficient to allow for an accurate comparison. The claim “ST. MORIZ UK’S NO. 1 TAN” was considered misleading because it was not clear if the advertiser’s sales figures were accurate, or if the data had been collected, presented, and applied in a different way to that of its competitors. In addition, the data had been subject to masking, whereby some retailers did not provide details about the volume of sales for certain products as this was commercially sensitive information. The data, therefore, was considered unreliable (Hothouse Partnerships Ltd, 18 April 2018).


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, “no.1” claims are likely to be understood as comparisons with identifiable competitors. 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. 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.

A complaint about an ad for a kitchen supplier which stated “The UK’s number 1 Kitchen Retails Specialist” was upheld because, whilst the advertisers could substantiate the claim, the ad did not include any information which would allow customers to verify the claim (Wren Kitchens, 26 July 2017). See also ASTOK Ltd, t/a TVBet, 15 April 2020.

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

Is sales data always required?

Whilst in most cases a best-selling “number 1” claim should be supported by sales data, in some circumstances, marketers may be able to substantiate the 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).

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