Instead, when making speed claims in broadband ads, providers should base it on the download speed available to at least 50% of customers at peak time and described in ads as "average".
This takes effect on 23 May next year after a six-month implementation period and will apply to residential broadband services.
This decision to change regulations follows research by the Advertising Standards Authority into consumers’ understanding of broadband speed claims.
The research showed that consumers are likely to be materially misled by the way speed claims are currently being advertised.
CAP then carried out a full public consultation which strongly indicated that a change to the current standards was supported by evidence and all key stakeholders.
After this, CAP consulted with major ISPs, a trade body representing over 200 ISPs, consumer groups, think tanks and Ofcom.
Respondents unanimously supported change, with most arguing for median speeds measured at peak time, to be described as "average" or similar in ads, as the recommended basis for speed claims.
Most respondents also favoured a single figure over a range and a peak-time measure over a 24-hour measure.
CAP considers that median peak-time download speed is the most meaningful speed measure to customers because it is easily understood and allows for consumers to make comparisons between different ads that they see.
If broadband providers were to advertise a range of speeds, customers will not know where in the range they fall at all, or may interpret it as the speed they are likely to get individually.
Likewise, a peak-time measure provides a better indication of actual speeds consumers are likely to experience.
CAP considered that a 24-hour measurement has the potential to mislead consumers by not providing an indication of the speed they are likely to receive at the time when people use the internet the most.
"There are a lot of factors that affect the broadband speed a customer is going to get in their own home; from technology to geography, to how a household uses broadband. While we know these factors mean some people will get significantly slower speeds than others; when it comes to broadband ads, our new standards will give consumers a better understanding of the broadband speeds offered by different providers when deciding to switch providers," director of the Committees of Advertising Practice, Shahriar Coupal, said.
The ASA has also decided that it is not materially misleading to describe broadband services that use fibre-optic cables for only part of the connection to consumers’ homes as "fibre broadband" following a review.
It published research carried out by the agency, Define, which found that "fibre" is not one of the priorities identified by consumers when choosing a broadband package; that consumers did not notice "fibre" claims in ads; that consumers, when probed, saw it as a shorthand buzzword to describe modern, fast broadband; and that consumers did not believe they would change their previous decisions after the differences between those services and broadband services that use fibre optic cables all the way to the home were explained to them.
However, in recognition of the performance differences between different types of broadband service, including between "part-fibre" and "full-fibre" services, the ASA advises that ads should not describe non-fibre services as "fibre".
Ads should also not state or imply a service is the most technologically advanced on the market if it is a part-fibre service, and if they should make performance claims they should be appropriate and substantiated.
Specifically, ads should refer to speed in a manner that is appropriate for the technology, including by having due regard to CAP’s new guidance on numerical speed claims.
"We continually review our standards to make sure they reflect consumers’ experiences, the technology available and the evidence base to make sure our standards are in the right place. Following extensive research and consultation, we hope our new standards will improve customer confidence in future ads," Coupal said.