hello, i have recently been married to my tgf we will be trying to go for settlement visa next week , my question is , my wife has changed her last name on her thai id card , does she also have to change her passport aswell, any help would be great thanks

I don't think she has to change her surname but her visa application and TB certificate etc must be in the same name as the one shown in her passport.

As Sumrit said but.......She could get the name change endorsed in her passport for free or even get a new passport for a little over B1000.

Remember if your settlement visa is successful the only ID she will have in UK is her passport so for opening bank accounts, getting NI numbers etc she will be using her Thai name, nothing wrong with that but maybe that is not what you intended.