BT have it in the contract that your broadband connection cannot be used for illegal stuff and can cancel your contract for any such use with no refund so if anyone does use it bang your done if they can be bothered to go after you which before you did this post was slim but now I doubt you'd last long before you get the first letter please cease your activerties as they do sometimes give a warning I know this from friends who have done things in the past.
To be honest if I where you I'd not bother. unless Like I said before you could get a contract thats a month long and with another provider so if you do get banned it's just from that provider, BT own pluss net by the way.
Why do you want to set your own node up?
You do know pleading ignaronce wont stop them confiscating your equipment.
There's a risk that anyone operating a Tor node would fall foul of the Acceptable Use Policy http://www2.bt.com/static/i/btretail/panretail/acceptableuse/ which is called up from the BT Residential Standard Terms.
The problem is that many people use Tor for transferring illegal material, and so anyone who operates a Tor node is probably transmitting or receiving illegal material without knowing it.
I've been running a relay for almost 2 years on BT Infinity, never heard a peep from them about it. Before that I ran one on O2 Broadband. Sometimes a bridge, but never an exit node node. Running an exit node is just too risky in this country I think from a legal point of view.
You will have to do port forwarding on your router and open ports on the computer's firewall so there is a small security risk from that you will have to bare in mind if you decide to proceed with it.
Hello NSA and GCHQ by the way