Hi,
The thing with Thailand is that its very easy to spend lots of money especially if around the nightlife.. Sometimes people have this impression that Thailand is dirt cheap but that fact that it is semi developed means you can still get those home comforts that you want but they cost as much or more than they do at home (sat TV, imported fruits, wine, etc)..
Theres been lots of budgeting discussions and posts. but to make it very brief.
Outside Patong.. Living a normal life.. Cooking for yourself.. Not being extravagant.. Living like an old retired person... you could manage for 35 - 40k baht per month. However thats once you know the lie of the land and how to get stuff the right price etc. initially always hurts a but to get set up.
Inside Patong or the touristy areas I think you need to raise that to about 60k baht to live a fairly quiet life, go out once or twice a week (maybe more if your a light drinker.. If I go out I come home at dawn with lots of money gone.. Thats what I like about the nightlife here).. For this you start to live a nice lifestyle, you have what you need, you have some money for meals out, nice wines, some social activity but your not going mad either, your still money concious.
Once that comes to 80k baht per month you can live in Patong in a nice house or apartment, not worry or think about about money as much, be out 5 or so times a week, eat at resturants a lot, butterfly about with lots of girls, generally have a great time and a (un)healthy lifestyle.
Over 80k it depends on the person.. Its much eaiser than you would think to spend a lot.. I spend well over the numbers that I have mentioned and dont mind that one bit, I feel I get my moneys worth and enjoy a level of lifestyle that I simply couldnt get for what I spend back home.. I have my western comforts, and what Asia has to offer.
8k GBP = 550 - 570 depending on rates.. That comes down to under 50 per month and is tight to really cut lose but I am sure it could be done and would still be enjoyable.. Much of that depends on you.. Money runs away fast on drink and women but if your into sports or other things for your time you may be ok.
Me I would do a awful lot to try to add 2k GBP to that 1 year account.. The fun I would have with 60 per month is a LOT higher than the fun I woiuld have with 45.. That little bit makes quite a difference IMHO.