Broadband speeds in the UK are much slower than advertised by internet service providers, a study by Computeractive magazine has found.
What broadband speed are you clocking up?
Some 3,000 readers took part in speed tests and 62% found they routinely got less than half of the top speed advertised by their provider.
It is the latest in a series of questions over the way net firms advertise broadband services.
Regulator Ofcom said it was aware of the issue and was "investigating".
The figures were gathered from more than 100,000 speed tests that the 3,000 respondents carried out to build up a picture of their average net-browsing speed on ADSL lines.
Statistics about net users in the UK show that half of current broadband users receive ADSL services that should run at speeds between one and four megabits per second (mbps).
The other 50% are on deals offering up to eight mbps but the tests revealed that, in reality, very few achieve the top speeds.
"This problem has been building for a while with a growing gulf between what is advertised and what is delivered," said Paul Allen, editor of Computeractive.
"The adverts often have super-fast broadband in huge lettering with the "up to" clause in very small print," he said.
"Users who have taken the test were surprised at the size of the gulf," he added.
Broadband is often not as fast as advertised
Some 28% of the 3,000 respondents who took the ADSL speed test found that they received less than a quarter of their maximum advertised bandwidth.
While consumers may currently not notice their sluggish connections, this could change thinks Mr Allen.
"Previously it has not been a massive issue but in the coming year we are entering the net TV age and video content is bandwidth-hungry," he said.
Mr Allen called on regulator Ofcom to provide an independent speed test to anyone who has signed up to receive broadband.
Speaking for the telecommunications watchdog, a spokesman said: "We are looking at this issue. It is not a huge driver of complaints but it has come on to our radar screen."
"It's about the difference between the headline rate and the rate received," he said.
The spokesman said Ofcom was working with the net industry and other organisations such as Which to investigate the extent of the problem and what can be done about it.
"Once we have carried out this work we will assess what options might be available to tackle it," he said. The results of the investigation would be made available in the "near future", said the spokesman.
Research by market analysts Point Topic sugggests that, in many areas of the UK, few people will be able to get the fastest broadband speeds.
Only 5% of the population will be able to enjoy speeds of 18Mbps. More than half will only be able to get 8Mbps.
People are using more bandwidth-hungry applications
Ofcom was also working with the Advertising Standards Authority to keep an eye on how net service firms word their marketing materials.
"We make sure broadband advertising does not advertise speeds that cannot be guaranteed," he said. "They have to make it clear that there is a best possible speed rather than an average speed."
The ASA has investigated several cases of misleading promotions, most recently asking Bulldog to make it clear in its adverts that speed was dependent on how far away from the exchange people lived.
It ruled that broadband providers could use the words "up to" 8Mbps when describing services as long as customers were likely to get close to those speeds.
A survey last month by consumer group Which found that consumers with services promising speeds of up to 8Mbps were actually getting an average speed of 2.7Mbps.
There are many variables that determine the speed of a connection, including how far away from the telephone exchange the line is, how many others are using the line at the same time and the quality of the wiring within a home.
The tool used in the study is available for download from the Computeractive website. It was developed by advice service Broadband Choice.
Computeractive has also launched an e-petition on the Downing Street website, asking the government to force net service firms to provide clear information about the typical speed users will receive alongside the maximum speed.