By Jason Palmer
Science and technology reporter, BBC News
The material used to deliver broadband is a big contributor to speed
Broadband users are not getting the speeds they are paying for, according to the largest survey of its kind ever undertaken by telecoms regulator Ofcom.
Nearly one fifth of UK broadband customers on an eight Megabit per second (Mbps) connection actually receive less than 2Mbps, it found.
The research showed that less than 9% of users received more than 6Mbps.
However, the report shows that average connection speed across the UK is 4.1Mbps, up from 3.6Mbps in January.
The UK government would like everyone in the country to have access to broadband speeds of 2Mbps by 2012.
"It's very easy to go out and find out what the price of broadband is, but much more difficult to get a good understanding of what the observed speeds are likely to be," said Ofcom chief executive Ed Richards.
The report also ranked the average speeds of nine major UK ISPs, with Virgin Media - which primarily operates in urban areas and uses high speed cable networks - coming out on top.
In order to address the issue of speed, Ofcom worked with Samknows, a broadband measurement firm that specially modified the routers that decode the signal coming into subscribers' homes.
While many websites offer speed tests, their results can vary widely due to a number of factors aside from the ISP's speed; the routers measure the ISP's delivered speed regardless of these factors.
The routers collected speed data from 1,600 users' connections nationwide between November 2008 and April of this year - amounting to some 60 million separate speed tests in all.
The numbers were then adjusted for a given user's distance from the telephone exchange. For broadband that comes through traditional copper wires, such as ADSL, the measured speed is lower for users who are farther from one of the country's 5,800 exchanges.
The speed study was accompanied by a survey of subscribers, finding that although more than 80% were satisfied overall with their service, about a quarter said the network speed was not as fast as they had expected.
Because the measured speeds varied so much, a simple league table of ISP speeds is difficult to make.
However, Ofcom released a table which shows comparisons for nine major ISPs, showing which are faster and slower.
HOW UK ISPS COMPARE
||...is slower than...
||...is faster than...
|All services at 8Mbit/s except Virgin Media at 10Mbps
||O2, Orange, Plusnet, Sky, Talktalk, Virgin Media
||O2, Virgin Media
||AOL, BT, Tiscali
||BT, O2, Orange, Plusnet, Sky, Talktalk, Virgin Media
||AOL, BT, O2, Orange, Plusnet, Sky, Talktalk, Tiscali
"The Ofcom study is important as it quantifies accurately for the first time what consumers have known for a long while - namely that you are extremely unlikely to receive the advertised broadband speed," said Charlie Ponsonby, chief executive of broadband comparison site Simplifydigital.
"Also for the first time it makes a robust, like-for-like comparison between broadband providers."
However, BT, who ranked lower in the survey, criticised the report.
It said the sample size was too small and the results were "unreliable".
In particular, it said that because it provided rural broadband its average speed was bound to be slower than other ISPs.
"We have many customers whose lines are at the limit of broadband service, with resulting lower average speeds," it said in a statement.
The Internet Service Providers' Association (ISPA) also questioned why the report was limited to larger ISPs.
"It is disappointing that the research does not reflect the breadth of the industry," it said in a statement.
It also pointed out that the number of households unable to get speeds of 2Mbps (megabits per second) or above is far higher, at 19%, than the 11% suggested by the Digital Britain report.
This, it said, made the government's challenge to bring the nation up to speed even harder.
Ofcom's strategy and markets developments partner Peter Phillips stressed that the two major contributors to the measured speeds from a given provider were the type of technology that they employed, and the number of subscribers on that provider's network.
Typically, broadband provided by a cable connection outpaced that provided by copper wire-based ADSL.
However, the number of users on a given network played a strong role, so that a first-generation ADSL network with little traffic could record higher speeds than a newer, ostensibly faster ADSL2+ network.
But Mr Phillips said that this makes the broadband market a dynamic one.
"The broadband market is continuing to evolve as ISPs invest in their networks, driven by consumers' demand for faster and better broadband," he said. "Those that are investing more are clearly delivering a better service."
Ofcom admitted that it would need to carry out such tests again in order to reflect the changing infrastructure and subscriber base, but a spokesman told BBC News that Ofcom currently had no plans to launch another study.
For now, the watchdog is looking into assessing the degree to which customers are aware of what they are buying when shopping for an ISP.
Of the UK's nearly 200 ISPs, 50 - comprising 95% of the UK's broadband subscribers - have signed up to Ofcom's voluntary code of practice.
The agreement encourages ISPs to disclose more than just the "maximum possible" speeds to prospective customers.
"It is critical that people are told when they're new customers what speeds they can reasonably expect," said Mr Phillips.
Ofcom is currently undertaking a nationwide "mystery shopping" exercise, approaching ISPs as potential customers and assessing whether they quote reasonable speeds.
Results of the study are due out in the next few months.