I've just got my new British passport after losing my last one. My visa has gone over now and obviously I don't have my old passport to 'transfer' it.

Can I just go to Nong Khai immigration (on my way to laos) and they can 'update' the details, I pay my overstay and exit?

 

It depends upon how long your overstay is.

You will need a copy of the police report  for the lost/stolen passport when leaving the country.

You would pay the overstay fine at the bridge.

It will be 82 days when I go. I have the police report. Do you think it will all be cool?

Nong Khai will normally clear long overstays.

Your fine will be 20k baht.

Thanks for you help..as long as I wont get sent back to Changwattana..

2 hours ago, justaphase said:

Thanks for you help..as long as I wont get sent back to Changwattana..

This is a case where a "visa-run" company with experience in this could be helpful.  If stopped en-route at a checkpoint - or any time before you clear your overstay - you could be arrested and sent to the IDC.  I am guessing those companies have arrangements to avoid this outcome.