In my own experience,,,,,,
The prices given on-line with Thai are not the same as your agent can get, its allways worth asking then comparing before you make up your mind.
For the uk guys i recommend
www.trailfinders.com we have got several tickets from them , to many destinations, pretty cheap, they have offices all over uk, they will need a copy of your credit or debit card .
Im checking today, waiting for a fax from Thai about the miles, Website claims to have a promo on for round the world tickets, so im gonna try to book Phuket-Lhr -montreal - Seoul - Hong Kong - BKK - HKT, then they say if you buy any ticket in one hit you can use your complimentary upgrade voucher ( you get one every time you hit 50k in 1 yr ).
So i guess if your gonna milk something go for it big.
Ill post the reply on how many miles they give me on a promo ticket using an upgrade voucher, 150 % would be nice,lets see.