how do I do this - need to do it because existing ballcock is covered in limescale and toilet flushing very slowly

speedball1

Changing your ballcock will not solve your flushing problem. Let's g et this over with one post. Describe how the toilet flushes and I'll instruct you on changing the ballcock along with solving the flush problem. regards, toim

definitely foxed

Had another look and - incoming water into the cistern is coming in slowly - not usually like this

speedball1

Describe your ball cock. Float ball on a rod or a can on a wire.

definitely foxed

it is a ball with a rod - lots of limescale in the cistern too