I would get the process underway before you come down because you will need certain documents from your existing doctor and police as part of the application process.
I suggest you get in touch with the BTB direct who, in my experience, are helpful. Establish an email link with them and you can move forward. We got our QRP without having to use any local adviser, albeit this was some 8 years ago but I doubt it has got more difficult since then and may in fact have got easier. The person to contact is, I beleive, Roshel at firstname.lastname@example.org