Hey jo.... to be honest mate it ordepends on what type of wall they are on. The adhesive that is used to put these tiles up goes off rock solid. if its a solid wall then i would get an old chisel or something with a point on that u can belt with a hammer. Try givin it a good whack near the center, if it goes then perfect, u can start levering off the broken bitsout from the center. But these tiles dont always break easily, if it wont break then try nearer the corners and do bit by bit and lever it off the wall. U will be it for a bit of a suprise if the wall is a stud wall with plasterboard and thin skim as this operation will prob wreck the boards behind and u will be left with a huge hole, and at worst u will fracture the adhesive of other tiles and make a right old job for urself.
Whichever way u do it mate be carfull and wear some safty glasses as porcelain will more than likely spliter and flake so watch ya eyes ....
Hope this helps mate, oh and dont forget to send ur plumber ya bill!!!!!!:lol: