The UK's average actual fixed-line residential broadband speed has increased by over 25 per cent over the past year from 4.1Mbit/s to 5.2Mbit/s as ISPs increasingly move to offer higher speed broadband packages, according to Ofcom's broadband speeds research, conducted in partnership with broadband monitoring specialists SamKnows.

The study shows that nearly a quarter (24 per cent) of UK fixed-line residential broadband connections had a headline or advertised speed of above ‘up to' 10Mbit/s in May 2010, compared to just 8 per cent in April 2009.

However, the move to faster headline speeds has led to a growing gap between the actual speeds delivered and the speeds that some ISPs use to advertise their services. Differences between headline and actual speeds are often caused by broadband being delivered over copper lines which were originally designed for phone calls, hence speeds slow down over long and poor quality lines, and because of electrical interference.

Ofcom has strengthened the Voluntary Code of Practice on Broadband Speeds which it introduced in 2008. ISPs who sign up to the revised Code commit to give consumers a more accurate and consistent estimate of the maximum speed likely to be achievable on their line.

ISPs also commit to help consumers improve their speeds and give consumers the option to leave their contracts early without penalty (within three months of signing up to the service) if they receive a maximum line speed that is significantly below the estimate they are given at point of sale and the ISP is unable to resolve the problem.

Some ISPs have in the past year moved away from advertising their services on the basis of ‘up to' headline speeds but others continue to do so. Ofcom has discussed this issue with the Advertising Standards Authority and the Committee on Advertising Practice who are currently undertaking a review in this area.

Ed Richards, Ofcom Chief Executive said: "Ofcom's research shows that average speeds have increased which is good news, but there is scope for a further step change in the quality of the UK communications infrastructure.

"Actual speeds are often much lower than many of the advertised speeds which makes it essential that consumers are given information which is as accurate as possible at the point of sale; this is what the new Code is designed to deliver. We are delighted that all major ISPs have signed up which is a major step forward."

The Communications Consumer Panel welcomes Ofcom's plans to strengthen the Voluntary Code of Practice on Broadband Speeds as a positive move to improve the service and speeds that consumers get.

However, Anna Bradley, Consumer Panel Chair, said: "The code leaves it to consumers to find out what speed they are getting. We believe that there should be greater emphasis on ISPs to provide even more practical support to consumers. That's why the Panel is calling on ISPs to go back to consumers within a month of their contract starting to tell them what actual speeds they are getting, giving them a discount or moving them to a lower cost package if they aren't getting the speeds they were expecting."

John Petter, managing director of BT's Consumer Division, said: "We support Ofcom's Code but want to go even further and are investing further in systems to make our predictions even better - and to have them confirmed in writing.