BT overcharged its rivals £95m between 2006 and 2011 - and will pay the excess back to TalkTalk, Virgin Media and others following an Ofcom probe.

There were three investigations in total: one was triggered by Verizon UK, another by Cable & Wireless and the third by an aggregation of ISPs including TalkTalk and Sky.

They all claimed that since April 2005 BT overcharged for its Backhaul Extension Service (which connects unbundled exchanges to an ISP's network) and Wholesale Extension Service (connecting bits of the network together), both of which are provided by BT for a one-off fee and ongoing rate, and it's this rate that Ofcom feels was exceeded.

Not that the communications watchdog jumped to that conclusion; its investigation started in September 2010 and involved appeals and counter appeals as well as additional evidence from BT as it sought to justify the charges.

And it's not over yet.

"We are disappointed with Ofcom's determination that we overcharged," the national telco told us in a statement. "We are considering all options available other us, including appealing."

Ofcom issued a draft decision eight months ago, and this final ruling is much the same so it isn't that much of a surprise. BT is keen to point out that it has the money stashed away just in case it loses or decides against prolonging the process any further. ®