Use of Sky for any commercial or business purpose is NOT permitted.
So, you have a choice of one.
Thanks for all the feedback. The business use issue would appear to apply to both.
From Sky T&Cs
"Sky Broadband is for private use by you and members of your household only. It must not be used for any commercial or business purpose."
From BT T&Cs
"The services and equipment we provide to you under these terms must not be used for business purposes."
I'm sure they're just covering themselves so a customer can't claim compensation if the service does an O2.