It would seem to suggest that fasthost have possibly misconfigured the IPv6 DNS information for your site and when the preferred connection is via IPv6 it fails.
just tried and success - you've cracked it - brilliant thanks
not certain where to go from here though
and what happens to anyone else trying to connect through BT - not that there's a lot of traffic through the site but it would be good if BT could access it who has IPv6 enabled
so it's looking as if if it could be BT's IPv6 rollout ?
Great detective work.
Received this morning
What they don't seem to understand is if the website resolves to an IPv6 address it should work!! If it only resolved to an IPv4 address , then yes, that would be fine.