Your first step is to apply for a basic disclosure to disclosure Scotland and see what's on there. There is no point discussing this until you know that.
Yes there is the Rehabilitation of Offenders act, but Ian Huntley effectively ended that.
If something is on there that is not necessarily the end, it may be that you would be able to apply to the cheif constable to have it removed but of course you'd be best advised contacting a specialist lawyer about that, and that means a city centre large firm.
First job is to apply for the form, the system is fantastic these days, cheap and fast, as many people need to apply for all manner of jobs. There is a monumental fudge at work because Scotland has a completely separate and more lenient legal system. Good luck
This is nothing to do with the Bangkok consulate. Visas are only issued in Britain, and the process is amazingly easy, follow the website Tod posted and you should have a new passport very soon. I did it in 2015, and it was a great and very efficient service. Good luck.
Actually the international job fell through for seperate reasons, but yeah the lady who issues the wps said it was not going to be a problem as both jobs qualified.