More than 50 percent of ADSL broadband users can only achieve half the download speeds promoted in ISPs' 'up to 8Mbps' adverts, according to the largest survey of its kind ever undertaken by Ofcom.
What's more, research by the telecoms regulator found that that the highest download speed someone with an 8Mbps package can achieve is actually 7.2Mbps.
The figures have been released following an Ofcom study earlier this year based on 60 million performance tests in 1,600 homes.
Fewer than one in ten households with packages of 'up to 8Mbit/s' received actual average speeds of more than 6Mbit/s, while one in five had to make do with less than 2Mbit/s.
The average download speeds achieved in April were 4.1Mbps. However, this was an improvement on January, when average speeds were 3.7Mbps.
ISP and package - Average speed
AOL ('up to' 8Mbit/s) - 3.3 to 3.9Mbit/s
BT ('up to' 8Mbit/s) - 3.8 to 4.2Mbit/s
O2 ('up to' 8Mbit/s) - 4.1 to 5.1Mbit/s
Orange ('up to' 8Mbit/s) - 3.8 to 4.5Mbit/s
Plusnet ('up to' 8Mbit/s) - 3.8 to 4.9Mbit/s
Sky ('up to' 8Mbit/s) - 4.0 to 4.7Mbit/s
Talk Talk ('up to' 8Mbit/s) - 3.8 to 4.6Mbit/s
Tiscali ('up to' 8Mbit/s) - 3.2 to 3.7Mbit/s
Virgin Media('up to' 10Mbit/s) - 8.1 to 8.7Mbit/s
The study also highlighted the broadband slowdown in rural areas. Ofcom said average speeds were 4.6Mbps in urban areas, compared with 3.3Mbps in rural areas.
There was good news for Virgin Media, however. Ofcom said average speeds on the company's ‘up to 10Mbps' cable broadband network were between 8.1Mbps and 8.7Mbps, twice that achieved by ADSL users.
"As the Ofcom speed tests show, Virgin are the best bet for a package that delivers on speed and this is a result of significant investment in their network," said James Parker, broadband manager at MoneySupermarket.
"People need to check how their providers fare when picking a broadband package, as the Ofcom test shows, the faster products can often be poor value for money."