On average, Brits are getting less than half the broadband speed they pay for, says Broadband Genie.
According to speed tests conducted by the broadband comparison site, consumers are getting just 45.8 percent of their headline speed.
Broadband Genie said Virgin Media and TalkTalk were the best performing of the ISPs tested, offering consumers on average 58.8 percent and 52.6 percent respectively of their advertised headline speed. However, the comparison site said this was likely because customers thinking they were on 1Mb and 2Mb packages clearly had better connections.
A Virgin Media spokesperson said: "We have been upgrading our cable customers' speeds regularly to improve the service we provide. In 2007 we upgraded 10Mb customers to a super-fast 20Mb, and in 2008 we upgraded our 4Mb customers to 10Mb, both for free. This year we're upgrading our 2Mb customers to 10Mb, so our entire customer base might actually find themselves on a speed much higher than they originally subscribed to."
"We are extending our network to more exchanges, supplying broadband to a huge number of customers in rural areas and optimising line speed for each and every one of them," added TalkTalk.
Broadband Genie editor Chris Marling said: "No matter what spin the ISPs put on these results, the underlying truths are there for all to see. Consumers are confused about their broadband connections, and even when they do get a handle on what they should expect, they are only getting half of the 'up to' speeds that lead the advertising campaigns".
"Technology is improving all the time - the internet landscape is almost unrecognisable from a decade ago. But the speed of change does not excuse ISPs from the duty they have to their customers. Consumers deserve a more transparent, honest and informative broadband marketplace so they can make correct, informed decisions."
Broadband Genie said BT, AOL and Orange, were the worst performing ISPs with consumers only getting around 33 percent of their advertised speed.
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See also: UK broadband 4 times slower than South Korea