thanks Taz. I will apply for a new passport here and go into overstay. My contact at immigration says that's fine as long as its below 90 days. I have an appointment in Bangkok next week for the new passport. My visa runs out in 6 weeks so hopefully I'll have the new one in time. Otherwise I will get a temporary passport to leave if I run out of time
Thanks for all your help Ron. I have just received an email reply from HMPO and have asked for an appointment on the 30th of March which is the earliest available date.