What the ASA actually does
The Advertising Standards Authority is the UK's independent regulator for advertising, and it covers every medium: television, radio, print, posters, and everything that runs online, from a Google search ad to a sponsored Instagram post. It doesn't write the rules from scratch. It enforces the CAP Code, short for the UK Code of Non-broadcast Advertising and Direct & Promotional Marketing, which is drawn up by the Committees of Advertising Practice and sits alongside a separate code, the BCAP Code, for radio and television.
Most of its work starts with a complaint, either from a member of the public or from a competitor who thinks a rival's claim doesn't stand up. The ASA investigates, publishes a ruling, and if it finds against the ad, the advertiser has to withdraw or amend it. There's no fine for a first breach, but media owners and platforms are expected to withhold space from advertisers who ignore rulings, which is usually enough to make the point.
Codes are reviewed and updated periodically, so any specific rule quoted here is worth checking against the current version at asa.org.uk before you rely on it. For a wider view of who regulates what across UK advertising, the UK advertising regulation map sets out how the ASA fits alongside bodies like Ofcom and the ICO.
The CAP Code: the rulebook behind every ad
The CAP Code rests on a small number of principles that apply to almost every ad regardless of sector: advertising must be legal, decent, honest and truthful, and it must be prepared with a sense of responsibility to consumers and to society. Underneath those principles sit detailed rules covering misleading claims, substantiation, comparative advertising, and how ads treat children, health, and financial products.
Substantiation is the rule that catches out the most advertisers who haven't dealt with the ASA before. Any claim that could influence a buying decision, a price comparison, a performance figure, a "clinically proven" statement, needs evidence held before the ad runs. An advertiser who can't produce that evidence when asked will usually lose, even if the underlying claim happens to be true.
The rules most businesses trip over
Misleading claims and puffery
The Code draws a line between claims a reasonable person would take as fact and claims a reasonable person would recognise as opinion or exaggeration for effect, sometimes called puffery. "The best coffee in Bristol" is generally read as opinion. "Rated the best coffee in Bristol by 500 customers" is a factual claim, and it needs a survey behind it. Businesses that blur that line, usually without meaning to, are the most common source of ASA complaints.
Harm, offence, and under-18s
Ads must not cause serious or widespread offence, and they carry extra restrictions when children are likely to see them, whether that's through the media placement, the content, or both. This is why food and drink advertising in particular has separate scheduling and content restrictions, covered below, and why an ad that would be fine in a trade publication can still fall foul of the Code if it runs somewhere a younger audience is likely to encounter it.
Comparing yourself to a competitor
Comparative advertising is allowed in the UK, but the comparison has to be with products meeting the same needs, based on verifiable facts, and it can't unfairly denigrate a competitor's trademark, product, or business. Naming a rival directly raises the bar on evidence, not because it's forbidden, but because the claim is now specific enough to be checked.
Sectors with extra rules
Some categories carry rules well beyond the general Code, because the potential for harm is higher or because Parliament has asked the regulator to take a firmer line. An advertiser working in any of these areas needs to read the sector-specific sections of the Code before writing a line of copy.
- Gambling: strict controls on when and where gambling ads can appear, and on content that could appeal to under-18s or people vulnerable to harm.
- Alcohol: ads must not link drinking to social or sexual success, and must not depict people who appear to be under 25 in a way that suggests they're the target audience.
- Food and drink high in fat, salt or sugar (HFSS): subject to placement and scheduling restrictions tied to child audiences, on top of separate government rules on paid-for online advertising.
- Financial promotions: claims about credit, savings, and investment products need to be clear about risk and cost, and some financial advertising also falls under FCA rules in addition to the CAP Code.
- Health, beauty and slimming claims: therapeutic and efficacy claims need robust clinical or scientific substantiation, and claims about medical conditions face particularly close scrutiny.
Influencer marketing and disclosure
Where a brand pays, gifts, or otherwise arranges for someone to promote a product, the resulting content is an ad, and it has to be obviously identifiable as one. The ASA's guidance, developed jointly with the Competition and Markets Authority, expects clear labelling, such as "Ad" or "#ad", placed where a viewer sees it without having to click through or scroll. A disclosure buried in a string of hashtags at the bottom of a caption generally doesn't count.
This applies to the brand as well as the influencer. If you've arranged the content and it isn't labelled properly, the ASA can and does hold the advertiser responsible alongside the individual posting it, which is why the brief you give an influencer matters as much as the brief you'd give an agency.
What happens if you break the rules
The ASA can't fine advertisers directly, but the consequences of a ruling against you are still real. A non-compliant finding is published, searchable, and often picked up by trade press, and media owners, ad networks, and platforms are expected to stop carrying an ad once it's been ruled against, or to withhold future space from advertisers who repeatedly ignore the Code. For serious or persistent breaches, particularly around misleading claims in regulated sectors, the ASA can refer a case on to Trading Standards or a sector regulator with statutory powers, at which point the exposure moves well beyond reputational.
Most businesses never reach that point. The more common outcome is a ruling, an amendment, and a lesson about what evidence should have been held before the campaign launched.
Building compliance into your process
The practical fix is to treat CAP Code compliance as part of the brief. Before an ad runs, it's worth being able to answer a short set of questions:
- What factual claims does the ad make, and is the supporting evidence written down and dated?
- Could the media placement reach an under-18 audience, and does the content need to change if it does?
- Does the sector the ad sits in (gambling, alcohol, food, finance, health) carry rules beyond the general Code?
- If an influencer or third party is posting the content, is it labelled as an ad clearly enough for a viewer to see it immediately?
For campaigns with a meaningful budget, or claims that sit in a regulated sector, it's worth getting a specialist compliance or legal review before launch. The advertising glossary is a reasonable starting point for the terminology, and the advertising guides section covers channel and budget decisions that sit alongside the compliance question. If you'd rather talk a specific situation through, the contact page has the details.