Make sure that the full length of pipe is removed from under the floor, in the room, and not just plugged at the restrictor elbow.
It's a bungalow with breezeblock and plasterboard internally. The pipe runs across the loft, comes down behind the fireplace back panel and terminates with something like this: http://www.bes.co.uk/product/6~NG~43~43~-Restrictors.html
May I ask why you suggest removing the pipe?
John.