I am thinking of going to Nakhon Pathom immigration to extend my tourist visa, but have been told that it is not possible to extend a tourist visa here. Does anyone know if this is the case? Anyone with experience of using this office? Thanks.

You can extend the 60 day entry from your tourist visa for 30 day at any immigration office if you have a local address to put on the application form.

You can do it at the office in  Nakhon Pathom without a problem.

I can confirm, full service. Only one other customer in the office (though the half dozen or so staff seemed busy enough). In an out in 30 minutes.