Trying to set up a Pi as local network server including local DNS elicited a problem.
It didn't always work *at all*. Or sometimes it did. The problem proved to be it trying to use IPV6 which I don't have configured.
IN order to stop it trying to contact DNS servers on IPV6, the final solution (after having tried every other alternative: The reason for posting here is so that someone somewhere will find this and not have to do the same) was to place this magic spell in
/etc/bind/named.conf.local
// disable lookup over IPv6 server ::/0 { bogus yes; };
That cleared up a slew of s*it from the logfiles. It may not be the most elegant solution but it has JustWorked.
One logfile entry remained and that was down to an out of date /etc/bind/db.root in the installation package.
The up to date version is at