I have done this in the last couple of years, the exams needed are mentioned in the previous post.
With regard to the flying you do indeed get a fifty hour reduction which includes 6 hours off your ppl course. This makes the PPL course a minimum of 39 hours. If you find a training organisation that is happy to get on with it and you get the PPL in minimums this leaves 66 hours of hour building before you can start the CPL course at 105 minimum. This is relevant if you are wanting to roll straight into an IR as you need a minimum of 70 hours P1 to do a multi engine type rating and 50 hours cross country for an IR.
Good Luck!