Dear List I may have fixed this.
I replaced the pfSense NIC which was in hindsight intermittently faulty, that finally failed completely. It has been stable since, with no logged messages other than the standard "dnsmasq[489]: reading /var/dhcpd/var/db/dhcpd.leases" Clearly more time is required, however it is looking good so far, given a number of error messages were noted on a daily basis prior and now none at all... Intermittent faults are the worst.....!!! Thanks for the assistance provided. Kind regards David