BT Wholesale, the UK's largest broadband supplier, is calling for ISPs to quote average speeds instead of theoretical maximums in their advertising.

The move follows an independent survey suggesting that just 15 per cent of customers who signed up to 8Mbps packages actually get that speed, despite advertising claims of top notch performance.

BT Wholesale, which sells broadband services to ISPs, called on regulators draw up guidelines on how broadband speeds should be marketed by service providers.

Just over a third of BT's DSL Max customers are currently achieving top 8Mbps, but the rest are hobbled by factors such as poor equipment and distance from the exchange.

"The reality is if you are very far from an exchange or there are environmental factors your speed will come down and there is not much we can do in the short-term to address that problem," said Guy Bradshaw, general manager of BT Wholesale.

"The industry needs to join with Ofcom to agree a set of principles as to how these messages should be communicated and advertised so that the understanding with the consumer is as accurate as it can be."

Industry watchdog Ofcom is currently investigating the matter. "There are technical reasons why a consumer may not get the full speed of the package to which they have signed up," said a spokeswoman for Ofcom.

"But the key point is that consumers should be able to make an informed decision about what broadband package is best for them at the point of purchase. "