In reply to Jackwd: Seriously, don'y try this just by reading something on the internet. We don't want anybody giving us a bad name because of poor rigging.
There's a ton load of us in the North West that regularly highline in Liverpool or we travel to the slate quarries when we fancy.
Alternatively, if you're down south there's a load of trickliners that also dabble in highlining.
Best thing to do is to ask around in the UK Slackline Association on Facebook.
We recently did a quick little video for Sony if you're interested. Come join us.