Removing toilet soil pipe

I'm redecorating a cloakroom, which involves replacing the toilet and
tiling the floor.

The old floor covering is out. The toilet and cistern are gone.

The soil pipe came out horizontally and then turned 90 degrees down and
over what I presume is a clay pipe that then goes through the floor and
presumably off to the waste sewer.

The white plastic soil now will not budge - although I've not hit it or
pushed it too hard as I don't want to damage the clay pipe.

It looks a litle like this:

   http://www.ultimatehandyman.co.uk/forum1/removing-toilet-capping-off -
soil-pipe-t46606.html

except mine's horizontal and then turns 90 degrees down rather than being
up-and-down as in the photograph. My white soil pipe is also a larger
diameter than the clay pipe (so it fits over it).

How do I get rid of the old white plastic soil pipe?

What would be the consequence of hitting/pulling too hard and breaking the
brown clay pipe?

Thanks

Antonio
arcarlini@iee.org