Thankyouandgoodnight - here is a DeWalt Hammer Drill from my favourite tool shop (Machine Mart).
DeWalt Cordless
As the description says its useful for light chisseling tasks such as removing plaster up to 4200 beats per minute!
Its cordless too so easier to use.
Pricey at £310 though.
Your local plant/tool hire firm may also be able to suggest an alternative.
By the way is the plaster laid on lathe or directly on the brick? If it is laid on lathe its better just to smash it through with a heavy 5Kg hammer then saw through the lathes with a power saw (check for live wires first). Once you have the lathes cut through then just use a crowbar to lever the the uprights posts that the lathes are nailed to right off the wall. Watch out you do not stand on any nails that may go through your feet though. Extremely painful.
If the plaster is laid direct on brick then if you 'score' the plaster in square sections on the surface of the wall with a heavy guage knife before attacking with a chisel or hammer drill chisel. It will break off in decent sized pieces much more easily.
I do emphasise you must wear a dust mask and goggles though whatever you do.
As you soudn as though you have abig job there you will need a number of big truck skips and system for delivering the plaster out of the building as it is heavy to shift and bulky with it.
Good luck.