CPL/IR instructors are probably feeling the pinch just now as the health of the airline industry generally dictates how much business they have, could be why no one has responded yet.
So, I'm not speaking from personnel experience but...I believe that established IR instructors at FTOs probably make around £40k a year, those doing just CPL will be on much less, probably an hourly rate of £35/fhr.
It take quite a lot to get there, you'll need a CPL/MEP/IR and FI rating, plus i'd expect 1000+ instructional hrs at very poor salary. Then you need 30hrs P1 on an MEP which is the most difficult to get unless you do some air taxi work in between times. Then you need to remove the applied instrument, night and Multi restrictions from your FI rating. So it is a viable and a very good career, but you'd need to spend a lot of money getting the ratings (much more than for an airline job if you put at type rating aside), and endure PPL instructor salary for a few years to get enough experience to move on.