I need a new plastic overflow pipe for inside my toilet cistern?

My downstairs loo which admittedly is old needs a replacement for the broken plastic overflow pipe inside the cistern.`The pipe is 2cms in diameter and has a screw fitting on the lower end. This goes through a hole in the bottom of the cistern and is then screwed tightly to prevent leaks. If the level of water in the cistern is too high then it escapes through the centre of the tube on to the floor. There is an external overflow pipe but it doesn't look as if the internal pipe connects with it. The cistern is low level and is made by IDEAL STANDARD . The number "825" is next to the name.
I think I may be looking for a part from an old cistern which is being taken out as this fitting does not appear to be made anymore.