Chewitt i have had just the same hooha at our house with our hall,stair and landing covered int he stuff,i had it priced and apparently they need to remove it first then skim the walls we were quoted 5 days work at £1000.
I promptly got myself a steamer and set about the artex myself not having a spare £1000 lying about it is soooooooo messy but not as hard work as i imagined,hard work but not as bad as i expected once you get the heat going,as long as you work with the artex wet,dont sand it and dont try to chip it off dry as thats when its dangerous