Research by the regulator, which looked at telecoms providers with a four percent or above market share and at least 30 complaints a month, revealed it received 0.58 complaints per 1,000 customers in Q2 of 2011. However, Ofcom did acknowledge that there had been an improvement in their performance on last quarter with complaints falling from 0.81 per 1,000 customers.
BT Retail was named the second most complained about ISP with 0.47 complaints per 1,000 customers while Orange took third place with 0.37 complaints. Virgin Media was the least complained about ISP with 0.15 complaints per 1,000 customers.
When it came to landline service, TalkTalk was also rated the worst provider with 0.8 complaints per 1000 customers, although once again complaints had fallen 1.16 per 1,000 in Q4 of 2010 and 1.12 in Q1 of 2011.
BT Retail and Sky were named the second most complained about firms with 0.25 complaints per 1000 customers each while Virgin Media followed with 0.15.
3 was the most complained about mobile broadband provider, with 0.14 complaints per 1,000 customers and with 0.02 complaints per 1,000, O2 was the least complained about.
Ofcom said the increase in complaints against 3 appears was driven by issues regarding disputed charges and customer service.
TalkTalk said it was encouraging that Ofcom's data demonstrates, following the Tiscali integration, the service offered has significantly improved in the last quarter with the number of complaints as a percentage of customers dropping by over 50 percent.
"We're simplifying our business for the benefit of our customers and calls to our customer services teams are down 40 percent from this time last year. We're also connecting new customers much more quickly and efficiently, last year it took an average of 23 days, today a customer will be connected in 14 days (which is the minimum allowed due to the cooling off period)," the ISP said.
"We're committed to providing good service alongside our best value and, while we clearly still have lots to do, we're confident that our customers are beginning to see the benefits of the changes we continue to make.'