Just looked 68.91Baht to the £ I normaly change £10 in the airport for taxi etc as their exchange rate not as good as the money changers in town, go to any bank or shopping arcade have changed money in Tesco Lotus, also hotels give a lower rate so I give them a miss, hope this helps.
(I never change money to Baht in the UK, rate seems very low)

Better still read bangkokbob in post ''going to thailand november 2007'' he tell's much more. its two posts above this one.