Originally Posted by
Yoshi212
As others have stated you're doing nothing improper and as long as your ESTA is approved you shouldn't experience any problems. If it were me I'd go down to London early and do the Thai passport during the day and then fly to the US (if appointments are available) just to get that out of the way.
I think I will hold it off for now until the next time I go to Thailand. Only because I normally fly out of LCY on BA1/BA3 and the Thai Embassy is on the other side of town.
Should really have got it sorted before I moved out of London but didn't realise how fast time went by!