A lot of recipes you find on American-based BBQ sites call for sea salt. Personally I just use sea salt, however I just happened across a UK site advertising Kosher salt so I thought I'd post the link.
http://www.naturalsaltseller.co.uk/Kosher-salt-C81.aspx
I've never used this site, so no recommendation or anything, it's just the first time I've seen Kosher salt advertised in the UK.