@Martin *********
It works like this
You would go to Lao, log in to the online eVisa system, fill out the application, upload the proof of funds (your bank in the UK balance would work for this) upload proof you're in Lao (visa/entry stamp) upload the required documents (marriage certificate, wife thai i/d, wife house book listing) you would use the hotel address in Lao as the current address, you would use your thai address as your "permanent address", then apply, get the confirmation of having applied, GO to the consulate in person and pay for the visa (2000baht) then wait in Lao until it's approved or rejected.
For regular visas (Non-O, Non-B, Non-ED) they are pretty fast, (just a couple days really) for the processing time. Then you'd print out the eVisa they send you by email and show that with your passport when you enter thailand.
That'd get you stamped in for 90 days