ahh this is the site I was trying to remember earlier but couldn't remember the name. I knew it was a guys name but could only think of Tom's Hardware and google wasn't helping. Yeah I used that when I was looking for a new ISP and it led me to Zen. Been with them for about 8 years now and never had any problems. Good customer service and never had a problem with connection that wasn't a BT infrastructure issue, and they have a good fault tracker on their website.
I was with IDNet before them. Another really good ISP but at the time they were really expensive with a restrictive usage allowance that could easily bump up the bill. Couldn't justify staying with them but I don't know if they've changed their pricing since then. Both Zen and IDnet are good for not over-subscribing their lines which causes slowdown at peak times.