https://www.google.com/intl/en/ipv6/statistics.html
TL,DR: overall, a bit over 35% of traffic is v6, with the UK at just under 34%, so that's quite a decent improvement. Anecdotally, I recently put in a simple firewall state analyser at home which simply counts the output from "conntrack", and I'm seeing v roughly 3:2 ipv4:ipv6, so I would guess that the overall stats for UK's IPv6 traffic are being held back somewhat by the ISPs we already know about, if my family's usage is somewhat typical.
