Tiling a fireplace help please

Hi!

I have a horrible fireplace currently, one of those kit effects that you slot in a hearth and backplate that are imitation marble sheets, then screw on the mantle surround to secure.

My queries..

1. Both the hearth and backplate are cracked
2. I wish to tile both hearth and backplate
3. Do I have to remove both hearth and backplate plastic/mock marble sheet stuff?
4. If so, what do I replace it with to tile over? Or can I tile directly onto this horrible stuff?

the fire is a gas coal effect one.

Thanks! (hope this in right place!)

Just to add, here's some pics of what I am dealing with if that helps

Remove that sheite and come back when you know what's under it - you can't tile onto that stuff.

Thanks Will be back when I take it to bits the weekend!