Broadband companies will have to give customers a true picture of broadband speeds, at the point of sale, when a new code of practice from Ofcom comes into force tomorrow.

Providers covering 95 per cent of the market have signed up to the voluntary code, which is being introduced by the communications regulator after its research indicated that around a quarter of customers cannot receive the speeds they were promised.

James Parker, of Moneysupermarket.com, the comparison website, said: "This code should benefit consumers massively. It means that, where a provider has a number of deals available, customers will be put on the most appropriate one.

"It is well-known that advertised speeds are rarely achievable, and this should stop someone who can only get 3Mb paying for 16Mb."

Ceri Stanaway, of Which?, the consumer group, added: "In a recent survey, when we asked people what frustrated them most about their broadband service, slow or inconsistent broadband speed was their biggest bugbear."

Under the code, providers are required to provide consumers, at the point of sale, with an accurate estimate of the maximum speed their line can support. According to some estimates, only half of those on "8Mb deals", for example, can achieve that speed.

The maximum speed available to a household hinges on a number of factors, including its distance from a telephone exchange – the closer, the better – and the quality of telephone cable.

Providers have repeatedly come under fire from consumer groups for "misleading" advertising of connection speeds. Yesterday, the advertising watchdog upheld complaints against a campaign by Tiscali which touted speeds of "up to 8Mb", with the "insufficiently prominent" qualification that "top speeds vary significantly".

The new code also requires providers to clearly explain "fair usage" policies, which put limits on "unlimited download" deals.

Broadband companies that have signed up to the code include AOL, O2, Orange, Sky, TalkTalk, Tiscali and Virgin Media.

Mr Parker said that customers already on broadband deals – with any provider – should ask the company for a free speed check, and should request to be put onto a more suitable deal if their speed is falling far short of the advertised maximum.

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