Even though ISPs may offer 2Mbps or 4Mbps services, consumers will never receive a service that reaches these theoretical speeds - but BT scored the fastest service as a percentage of its theoretical maximum.
The survey covered 10 of the biggest providers but did not include cable companies NTL and Telewest, which use different technology.
It also did not take into account price, availability or customer service, focusing purely on performance over the past three months, said Gavin Jones of industry analysts Epitiro. "If people are considering which ISPs to go for, this would just be one part of the equation."
Epitiro did point out that the results of this test do not indicate which ISP is the best, or is the best value for money. Factors such as the price of a service or the level of customer support or satisfaction were not considered.