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 ASA is likely to regard a "number 1” claim in the same way as a “best-selling” or “leading” claim, unless the context of the ad clearly indicates another meaning.

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?

Are all “no.1” claims best-selling claims?

Can a “no.1” claim be subjective?


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 “number 1” 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 “number 1”  claims, which will be understood as best-selling claims,  it is likely that comparative evidence relating to unit-sales, market share, or both, will be required.

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 their global competitors (Rental Republic Ltd, 19 January 2022). In contrast, the claim “Europe’s number one airline” was not considered misleading, because the advertiser could demonstrate that,  over a reasonable period before the ads were produced, the advertiser had carried more passengers than any other European airline (Ryanair Ltd, 7 February 2018).

When making an absolute “number 1” claim, consumers are likely to understand this to be an entire market comparison, and advertisers would therefore need to 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 No.1 Trade Mark Service”, because the data used to calculate the number of trade marks registered by themselves and their competitors did not include lots of their competitors who may have registered a similar number or more (Trade Mark Direct Ltd, 11 April 2018).  Similarly, an ad for a hair clinic which claimed it was “officially voted Europe’s number one hair-loss, hair transplant clinic” was ruled against because it was unable to verify that it had been compared against all relevant hair loss and hair transplant clinics in Europe (The Hair Loss Clinics (NW) Limited, 20 December 2017).

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 their competitors. In addition, the data had been subject to masking, whereby some retailers did not provide their volume of sales figures for certain products, including St Moriz’s own product, as it was commercially sensitive. Therefore, the data was considered unreliable (Hothouse Partnerships Ltd, 18 April 2018).


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).

Marketers do not need to identify explicitly the competitor or product that they are comparing with to be subject to the rules on comparisons with 'identifiable' competitors, and the ASA’s interpretation of ‘identifiable’ competitors is broad. If a consumer can identify at least one competitor that is being compared, whether or not it is identified explicitly in the ad, this will mean that the comparative claims must be verifiable. In most cases, “no.1” claims are likely to be understood as comparisons with identifiable competitors and must be verifiable.

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 as much information as possible in the ad to ensure that consumers are able to check it for themselves, and include a signpost in the ad to information on the basis of the comparison. 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 this claim, the ad did not include any information which would allow customers to verify the claim (Wren Kitchens, 26 July 2017). Similarly, complaints about the claim "#1 World's Live-Games Provider" were upheld by the ASA, because the ads did not direct businesses to any additional information regarding the comparisons and explaining the basis for the claims (ASTOK Ltd, t/a TVBet, 15 April 2020).

See Comparisons: Verifiability.

 Is sales data always required?

Whilst in most cases a “number 1” 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 “number 1” 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).

Are all “no.1” claims best-selling claims?

Sometimes, the context in which a “number 1” claim is used will give the claim a specific meaning, and will not be considered a best-selling claim. The claim “NUMBER 1 FOR A LUXURY VALUE CHRISTMAS FEAST”, with text underneath which stated, “We compared prices on 11 luxury products. Choose frozen. Save Money. Beat the queues” was considered a price comparison, rather than a best-selling claim (Iceland Foods Ltd, 29 April 2020). Similarly, 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. To make this claim, the advertiser would have needed evidence to demonstrate that a range of networks had been compared across a range of objective performance measures for a representative sample of mobile data users from across the UK and that the advertiser had received the highest score of all the rated networks. Because the claim was a comparison with identifiable competitors, it should also have been verifiable. (Vodafone Ltd, 28 July 2021).

If the meaning of a “number 1” claim is ambiguous, this may also be considered misleading.  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, amongst other interpretations. Because the ads did not make the basis of the network performance claims sufficiently clear, the ad was considered misleading (EE Ltd, 08 April 2020). See also Telefonica UK Ltd, 24 February 2021.

Subjective “no.1” claims

Whilst there may be situations in which the ASA would interpret a “number 1” claim as being the subjective opinion of the advertiser, in practice, such claims will almost always be regarded as objective.

In 2013 the ASA held that evidence relating to awards won by a letting agent, along with information relating to its branches, staff, vehicles, internet data and lettings boards did not substantiate its claim to be “Derby’s No.1 Award Winning Agent” which was considered an objective claim (IMS Lettings Ltd, 17 April 2013). See Property: Sales and board counting and Property: Sales and the use of website data.

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