Personally I think buying in Thailand would be more advantageous for support and configuration (especially keyboard and language) for a native Thai, if it's going to be predominantly there. If it's equal or more use in the UK though then buy in the UK. Big C and the stores around always seemed to have good deals on every so often in Udon Thani if buying there eg http://www.bigc.co.th/home-appliance.../notebook.html.
Don't assume cheaper in Thailand, you could do price comparisons with the ones in the link to see whether cheaper or more expensive. Phantip Plaza in Bangkok is the only place I'm aware of where great bargains may be found, but you could end up with a wrong-un.