Just four per cent of people signed up to a 16Mbps package actually achieve that connection speed, according to research from broadband analyst firm Point Topic.
Its figures highlight the difference between headline speeds offered by ISPs and the actual speed of the connection, with only 15 per cent of those with an 8Mbps deal getting anything like 8Mbps.
Many ISPs cover themselves with an 'up to' prefix before the headline speeds in their advertising.
Researchers examined the connections of 4,000 customers of the 'big six' ISPs in the UK - BT, Virgin Media, Carphone Warehouse, Tiscali, Orange and Sky.
Sky was the ISP that got closest to providing the promised speeds, followed by Virgin Media and Tiscali. The Carphone Warehouse, which has two UK brands - AOL and TalkTalk - was next, followed by BT, with Orange bringing up the rear.
Point Topic did recognise the difficulty of providing the same speed to all customers.
"There are many variables that affect broadband speeds, distance from the exchange, contention, line quality and so on. It is a challenge to be able to factor all these into a calculation that gives you a reliable idea of the actual speed an individual connection will achieve," said Pamela Varley, research analyst at Point Topic.
Last December, industry regulator Ofcom said it would be looking into the issue of the way broadband speeds were advertised in 2008.
www.point-topic.com www.sky.com www.virginmedia.com www.tiscali.co.uk www.aol.co.uk www.talktalk.co.uk www.bt.com www.orange.co.uk
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