British carriers are failing to meet the network performance of their high-speed broadband plans, according to an Ofcom survey of ISPs.
The study, which canvassed 1,600 homes and performed 60 million service performance tests, found users were receiving average speeds of 4.1Mbps, well short of the average 7.1Mbps of plans sold by ISPs.
Overall less than one in 10 internet users on an "up to 8Mbps" package actually experienced speeds above 6Mbps, Ofcom said. For one in five online consumers network speeds were below 2Mbps.
The Ofcom report revealed that no broadband customers were receiving the top download speeds advertised by ISPs, with carriers withholding the delivery of the "headline speed" of 8Mbps for technical reasons.
In terms of performance ranking, Virgin Media was the best provider delivering speeds of 8.1Mbps to 8.7Mbps, to customers who subscribed to its "up to 10Mbps" cable broadband service.
Tiscali and AOL filled out the bottom of the table, delivering connectivity of 3.2 to 3.7Mbps and 3.3 to 3.9Mbps respectively on "up to 8 Mbs" services.
BT, which came third last in the survey, slammed its accuracy. "The small sample used in this survey and the measurement of line length from exchanges make the report unreliable. Ofcom's report is also out of date because we are transferring customers to new broadband technology, ADSL2+, which provides much higher speeds," a BT spokesperson told TelecomsEurope.
He added: "BT Retail provides broadband to customers in rural areas too; many other ISPs do not or cannot do this. This means we have many customers whose lines are at the limit of broadband service, with resulting lower average speeds."
Ofcom said a digital divide between country and city-based internet users had emerged, with rural speeds on average tracking at 1.3Mbps behind those in urban areas.
Overall the survey found that all consumers experienced a 20% performance slowdown on peak evening hours, with the report suggesting bandwidth-hungry services like the iPlayer were having an affect.