Did mine split between Taylor Aviation at Cranfield with Bob Moore(who is a tough but first class Instructor) and then next door at Bonus Aviation who again were a first class school, well organised, good fleet and upfront with exactly what the costs would be, nothing hidden.
I did all of my training in the twin, Seneca and the Seminole. I also went on tour across Europe with my Bonus Instructor as part of my training and so got to fly airways and real approaches rather than the rather repetitive standard training routes.
I did do an hour in the simulator but found it boring and as I was doing the IR for real flying not a tick in wannabee box I preferred to do it all in the aircraft.
I started the ground school with Atlantic but after feeling demeaned by them after being made to feel stupid over my apparent lack of 'basic' maths and the fact that their course structure is not very flexible I moved to CATS at Cranfield and completed the theory with a high 90% average at my own pace and schedule.
All exams were at Gatwick which was a royal PITA over the three sittings. Fortunately I did not have to re-sit any exams.
All in all the IR is not difficult my friend just did the theory in 4 months and the practical in a month.
Don't believe all the myths about hydraulics and fire extinguishers and don't get talked into doing the ATPL theory 'just in case' if all you want is an IR.