Comment 281 for bug 417757

Ok. I am pleased to say this has finally been resolved.
The last few things I tried.
http://www.debian-administration.org/article/Disabling_IPv6_under_a_2.6_kernel

Commenting out all references to ipv6 in hosts (shouldn't be necessary but I was desperate)

#Disable IPv6
net.ipv6.conf.all.disable_ipv6=1
net.ipv6.conf.all.accept_ra=0
net.ipv6.conf.etho.accept_ra=0

In sysctl.conf - although sysctl didn't recognise any of 'em so I doubt that was solution

I think it was that first link that recommends:
To disable IPv6 it should be as simple as adding the lines

alias net-pf-10 off
alias ipv6 off

to /etc/modprobe.d/00local (creating the file if it exists).