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.
It would be interesting to see a similar test in the US. For some reason we would expect our results to be pretty similar.