When I renewed UK passport 2 years ago, they did not cancel my current one until the new one arrived and only photocopies were sent with the application so unless that has changed the guys in Trendy building will not do any cancel until the new one arrives and you should have time to do the whole process before August
ok interesting so if they give you a bit of leeway then it isn't necessarily needed to do a marathon day visiting both right? If I go to chamchuri on Wednesday, get that all done and see what stamp / date they give me, I can then go to Chaeng Wattana before that date is up, correct?