It all depends on how much time you have to study/learn/practice exam questions... It's a lot of material to get through and a TON of online questions... I went through over 12000 questions which really REALLY helped.
When I did it in 2011 the UK CAA was still doing paper exams...! Which meant that once you wrote an exam, you would have to wait 3 weeks for results, which meant that you wouldn't be able to make the booking period of 2 week prior to the exam sitting, so you would have to wait for the next months sitting.
I believe that they are in the process of changing over to computer based examinations (or have already - someone can confirm) which would speed the whole process up by months
Get all your UK entry visas sorted out well before the exam dates.
I would recommend CAPT (Add on the right at times)
With regard to doing your flight test in another land, yes you can...
http://www.pprune.org/flying-instruc...ight-exam.html