i am a tiler, Tile experts ltd is my company, yes you can tile on plywood but you need to use polybond on it first, wait for it to dry then tile.
the cement board your talking about is called hardy backer board, which is made of concrete and fibre, chadwicks do not sell it nor do brooks, but there is a place here in dublin citywest that supply it and manufacture it, but irish tilers do not use it. ill see if i can locate them for you, i have there number somewhere,.