You often read comments of the gold plating CAA making the IR unachieveable to the average PPL - I'd just like to say that it is definitely acheiveable, the only real problem is that the 'gold plating' has added is to the cost - if you can afford it then it is doable.
In relation to the work that is required:
7 exams all taken at Gatwick on two days every two months, the same exams on the same days, they are multiple guess and are pretty easy. A lot of the stuff you will already know from your PPL but a fair amount is new, but nothing very onerous. Other than for MET I put minimal effort in reading the manuals nut mainly working through the question banks and when I say minimal I mean about 1 day per exam (plus 20 hours compulsory Ground School for all 7 subjects). So at a guestimate I spent about 10 days total (actaully that sound like too much) preping for the exams and 2 days taking them.
First exam was April and last in June.
You can start the flying training before you have had your results, but I decided to wait and started training in late july and had my 170a in mid October - other than the 170 all of my flying and SIM work up to the 170 took place at weekends (on 18 separate days).
After the 170a I had two more flights at weekends for brush up and practice while waiting for teh exam which was on a Wednesday.
No suprises in the flying or sim and nothing that a reasonably competent PPL could not handle.
All done in a single.
As I said, other than the cost it is very achievable. And as I fly for fun I have put it in my accounts as part of this years fun as I enjoyed every minute of it.