The only studio I ever had experience with was Jacksons @ Rickmansworth - So I'm out of date (slightly, they pulled it down about 15years ago).
If your friend had a 23 year lease, I wonder if he can't go to a rent tribunal over this proposed increase? - not quite sure of how this works in the commercial sector, but I would be amazed if the new landlord can just up the rent on this scale?