Just the IP won't do you much good; it's a Telewest Broadband IP address which probably won't be very static. I'm on broadband too and to get a new IP address I just switch my BB modem off and on again. So if you hack just the IP address there's a good chance you won't hack the people you're interested in and you just end up attacking someone who's completely innocent.

If you have specific dates and times, Telewest most likely log who had what IP when, so if you report the matter to the police they will have the necessary weight to get the relevant info off Telewest and you can pursue them through the courts.