I was just browsing for tents and came across this. Ellis Brigham in Manchester have an altitude training centre. It seems that you pay 30 quid to sit in an egg chair, strap a mask over your face and get a readout on how well you deal with altitude. I've always felt as though I slow right down in even relatively low altitudes and so this could be an interesting test for me when I start my preparation for Kilimanjaro. It's not being able to deal with the altitude that worries me most about the climb and if I don't complete it, it will probably be due to this.
The site also mentions that you can book a series of training sessions before you embark on a high altitude trip. It doesn't say how much this would be, but I imagine it will be quite pricey. I do like the idea of working out on the cross trainer with an oxygen depleting mask stuck to my face though. I wonder if this is what they mean?