25hrs is probably the average. I took about that long.
Get yourself a copy of FS2004 or FSX and practice all the procedures at home. This will save you many hours and much money. In flying generally, and in instrument flying much more so, one should never get airborne unless one already knows what to do. For example there is no point in going flying at £150/hr or whatever to learn to track a VOR if you don't know how to do it! In instrument flying, the workload is high and one learns very little. Learning how to fly the stuff is best done on the ground, and flying is for consolidation.
For the single written exam, yes by all means get the Confuser. One needs to get the flavour of the questions into one's head - the CAA always plays word tricks. But if you can fly the procedures you will pass the exam anyway. And if you cannot fly every single IFR procedure, you are wasting your time doing the IMCR because it does give you exactly that privilege.
If you can, get your instructor (he will need an IR for this) to fly the FAA IR 250nm cross country flight with you (3 different approaches on it) and sign it off in the logbook appropriately, because should you decide to later do the FAA IR, you won't have to do it again.