There are dozens of broadband providers who will connect you to the internet through a BT line. I expect that most of them wont penalise businesses. To find a few, use the "broadband" tab at the top. Hopefully you will find what you want there but another option would be mobile broadband which doesn't need any phone socket. You should also consider having the phone disconnected and using a mobile for the office phone.

I currently run an Air Training Corps Squadron, the building for which has a BT line into it for phone calls. The line is currently classed as a business line, even though we only use about £3 per quarter in calls and we are a registered charity and definately not a business! I would like to install Broadband on the line but the BT Business rates are far too expensive for the service provided. Therefore I have two questions:

How do I get the line changed from business to residential? I have tried phoning BT but I can only get the standard call centres who do not understand my request? Can anyone give me UK based contact details or advice?

Or can I swap to another provider that gives me a Broadband+Phone package whilst I'm on a BT Business Line, so I can ditch BT?