In its Broadband Speed report, Ofcom found broadband speeds were likely to differ widely between supplier and location, with rural areas receiving the lowest speeds. It found the average advertised speed was 7.1mbs while consumers actually received 4.1mbs.
Nine major broadband providers' services were tested as part of the survey. The worst was Tiscali, which although advertising 8mbs speeds, was only delivering between on average 3.2mbs to 3.7mbs. AOL, like Tiscali owned by Carphone Warehouse, came in with a similar score.
The best provider was Virgin Media, which advertised "up to" 10mbs and delivered 8.1mbs to 8.7mbs.
However, Ofcom found overall that fewer than 1 in 10 people received the advertised speeds.
The report has led to further calls from consumer groups for more regulation on how broadband providers can advertise their speeds. The Communications Consumer Panel, which advises Ofcom, has called for average rate to be used rather than 'up to' speeds.
Last year broadband operators signed up to regulating broadband advertising. The hope was to eliminate misleading information and ensure that internet service providers offer customers greater clarity.
Steps that fixed-line ISPs are required to take under the voluntary code include providing customers at the point of sale with an accurate estimate of the maximum speed the line can support and resolving technical issues to improve speed.
The Broadband Speed report follows a similar survey when Ofcom found broadband speeds differed widely when it came to region. London received typically the highest speeds and Northern Ireland the lowest.
ISP advertised speeds and average speed
Tiscali ('up to' 8mbs) 3.2 to 3.7mbs
AOL ('up to' 8mbs) 3.3 to 3.9mbs
BT ('up to' 8mbs) 3.8 to 4.2mbs
O2 ('up to' 8mbs)* 4.1 to 5.1mbs
Orange ('up to' 8mbs) 3.8 to 4.5mbs
Plusnet ('up to' 8mbs)* 3.8 to 4.9mbs
Sky ('up to' 8mbs) 4.0 to 4.7mbs
Talk Talk ('up to' 8mbs) 3.8 to 4.6mbs
Virgin Media ('up to' 10mbs) 8.1 to 8.7mbs
*Data for O2 and Plusnet should be treated with caution as sampled sizes were smaller than for other ISPs