Outdated copper wires mean 76 percent are not seeing advertised speeds.
15.4 million UK households are not getting the advertised speeds on their broadband packages, according to a survey by Which?.
The survey found that 74 percent of households with fixed broadband connections were paying for speeds that they never got, despite 90 percent viewing speed as an important factor in their choice of provider.
Only 17 percent of homes received average speeds matching the advertised level and 15 percent managed this during the peak evening period.
The providers were accused of breaking advertising guidelines, which state that only 10 percent of customers need to achieve the maximum advertised speed. Only 4 percent of customers on TalkTalk’s 17Mbps package and 1 percent on BT and Plusnet’s 76 Mbps deals, were getting the top speeds.
According to Steve Holford, of fibre broadband provider Hyperoptic, the limitations of UK broadband delivery run deep.
"Unfortunately the news from Which? that over 15 million Brits aren’t getting their advertised broadband speeds doesn’t come as a surprise," he said. "The discrepancy between advertised and actual broadband speeds is due to the fundamental flaw in the technology that is used to deliver the majority of broadband connections.
"Consumers are being misled into believing that they are receiving ‘fibre’ broadband, when really the fibre stops somewhere in the streets around their home – the broadband is delivered into their house via outdated copper lines, which accounts for the quality and distance degradation in speeds and peak-time slowdowns.
"Only true fibre to the home enables residents to connect to the internet at advertised speeds."
Which? revealed the survey results as part of the launch of a campaign to demand change in the way that broadband speeds are advertised.
Executive director Richard Lloyd, said: "It’s not good enough that millions of homes are so poorly served by their broadband provider with speeds that just don’t live up to what was advertised. Broadband is an essential part of life these days so people shouldn’t be persuaded to buy a package which is never going to live up to expectations."
A BT spokesperson responded to the survey, saying: "BT uses the method to describe our speeds that is defined by the Committee of Advertising Practice (CAP) and followed by all ISPs (Internet Service Providers). We’re very clear that customers should not rely on headline claims, but instead use the personal speed quote we give them at the point of sale, which is based on their own line.
"If they aren’t happy with this personalised speed they can decide not to buy from us; if they are happy with the speed, but find they don’t achieve it, we allow them to end their contracts in line with the Ofcom code of practice."