BT Openworld is the most complained about ISP in the UK, according to telco watchdog Oftel.

Oftel's report revealed the number of calls it received from 1 April to 30 September this year about companies in the fixed line, mobile and internet access markets.

In the residential voice market complaint category NTL was clearly out in front, racking up 0.8 complaints per 1,000 users compared to runners-up Telewest and NPower with 0.5 complaints. BT and Eurocall took joint third place with 0.4 complaints. All five companies came in above the industry standard of 0.3 complaints per 1,000 users.

Oftel receives around 100,000 complaints each year and, so far this year, 11 percent have been about ISPs.

"For the first time we have included ISPs in our complaints publication because of the increasing number of complaints received," said David Edmonds, Oftel's director general of telecommunications. "We received nearly 7,000 complaints about ISPs between April and September. Their inclusion in the publication is added incentive for them to address these issues efficiently."

Top of the ISP complaints category was BT Openworld with 1.6 complaints per 1,000 users, followed by Pipex on 0.6. Both came in above the industry average of 0.4 complaints.

Service providers Telewest, Freeserve and NTL all scored a respectable 0.1, while AOL scored less than 0.1 percent per 1,000 customers.

In the mobile complaints category 02 and T-Mobile both scored 0.2, while Orange and Vodafone came in at 0.1 — all below the industry average of 0.5 complaints per 1,000 users.

The full report can be viewed at here