morning chaps and chapesses, my son in law from the uk invited my family to the uk for christmas, as a surprise for his wife my daughter, all travel paid, wonderful gesture, so just 2 quick questions, my son has a uk citizenship, so its a new passport for him, my missus who's been to the uk twice before, so can the uk chaingmai consulate handle the necessary paperwork, or does it mean a trip to bigcock, errrr bangkok.

Bit confused by the way you have worded your post as to what nationality the various people are and where they are now, but will try to answer.

Anyone who is a visa national will need to obtain a visa before travelling to the UK. If not sure if someone is a visa national, you can check here.

Applications in Thailand must be made via the UK VAC in Bangkok. One can submit an online application but will need to attend the centre for biometrics to be taken and to hand in the supporting paperwork.

Anyone who is a British national and living in the UK whose passport has expired will not need to apply for a new one in order to sponsor a visitor. Their is no requirement for a sponsor to have a valid passport.

Obviously, though, if he is living outside the UK and wishes to travel anywhere then your son-in-law will need to have a valid passport. If he is living in Thailand then see Applying for a UK passport in Thailand. If living in some other country then check with the British embassy in that country.

Edit, just reread your post and see that it is your son, not son-in-law who needs the passport.

Edited October 4, 200916 yr by 7by7

morning chaps and chapesses, my son in law from the uk invited my family to the uk for christmas, as a surprise for his wife my daughter, all travel paid, wonderful gesture, so just 2 quick questions, my son has a uk citizenship, so its a new passport for him, my missus who's been to the uk twice before, so can the uk chaingmai consulate handle the necessary paperwork, or does it mean a trip to bigcock, errrr bangkok.

I've read this three or four times and I'm none the wiser as to who is from where, what relation everyone is to anyone else and where anyone lives.

Maybe it's easier for us non native speakers....

OP has been invited to UK for xmas by his daughters husband. Free tickets to OP and his Thai wife and their British/thai son.

He knows that he needs to get a passport to his son (actually he needs two, both thai and uk one) but is asking how to apply visa for his thai wife. Can he do it in CM or is travel to BKK required.

7by7 pretty much answered the question, however i would check with the VAC if it is possible to apply by mail. Can't remember now if it was aus or uk vac that has agent in CM so that you can submit and collect locally without the need to go to bkk...