Advertising regulators should change the rules so that the speeds available to customers in the middle of the range of actual available speeds is advertised at least as prominently as 'up to' speeds, it has said.

Ofcom's concerns come as it announced that though the average broadband speed actually received by users increased in 2010 it did so at a significantly slower rate than in 2009. Speeds were 5% faster in the seven months to December 2010 but had been 27% faster in the 13 months to May 2010, it said.

The current average speed of 6.2 megabits per second (Mbits/s) is just 45% of the average advertised speed of 13.8Mbit/s, it said.

The figures came from 765 million tests on the systems belonging to 1,710 users, said Ofcom. In its report on speeds, Ofcom said that slow speeds were still largely a result of the use of copper-based phone networks that were built for voice calls and "have been stretched to the very edge of their capability in order to provide broadband".

Other kinds of networks performed better, it said. "The highest speed cable services and fibre-to-the-cabinet services are consistently delivering speeds that are sufficient for virtually all applications likely to be used by residential broadband consumers," it said.

Ofcom published its views on broadband advertising, having submitted them to a consultation on the subject by advertising regulators the Committee of Advertising Practice (CAP) and the Broadcast Committee of Advertising Practice (BCAP).

It proposed a fundamental change to the way internet access is advertised.

"A Typical Speed Range (TSR) representing the range of speeds actually achieved by half of customers should be used when advertising broadband on the basis of speeds," it said. "If a maximum ‘up to’ speed is used in an advertisement, then the TSR must have at least equal prominence. Furthermore, the theoretical maximum ‘up to’ speed stated must be a speed actually achievable by a material number of customers."

Ofcom also said that companies should only be allowed to call a service 'unlimited' when it had no usage limits attached to it at all.

"We recommend [that] use of the term unlimited is only permitted where the service in question has no usage caps through a ‘fair usage policy’ or similar," said its response to the consultation (20-page / 246KB PDF).

The TSR should be the range of speeds experienced by the users who fall between 25% and 75% in the range of speeds experience by customers, Ofcom said.