Lot of us about,
I also work for HMG - I have managed to get everything part-time,
you have to throw leave at the problem but it is managable.
My advice would be to stay in, go to the states to get your CPL (or somewhere else sunny) within your leave period. You can get an FI(R) course part time and then build your experience. You have a three year window to get your CPL/IR after your exams.
The IR will be challenging to do within time as five weeks is the accepted norm. (Resettlement leave?).
If the picture suddenly improves with your CPL under your belt you can get your IR quite rapidly on the way out. - You've done all the hard slog of the exams, reward yourself with some flying!