If your Thai wife has been lucky enough to receive a permanent residence permit to reside in the UK with you as her UK husband for the rest of her life then this is an honor so it should be respected and not taken for granted.
A UK permanent residence permit is now given in a smart card form the same size as a credit card with a reference number printed on the card so no more need for visas and the next step if you choose would be citizenship.
The unwritten rule many people do not realize is that there is a rule about holding a UK residence permit which is you must not stay out of the UK for more than 2 years without returning to the UK or it is automatically cancelled and your Thai wife will be refused entry back to the UK.
So you must make sure that in a 2 year period you at least return to the UK for at least a holiday and do not stay out of the country for 2 years or more or face starting again at the beginning e.g. a UK settlement visa.
You would be surprised how many people make this mistake mainly if the UK spouse has retired and decided to spend more time in Thailand, SO BE CAREFUL!!! it is not for life if you make a mistake,
For more info contact [email protected]