Cat started to poo in the bath?

Hi all , we have a female cat , she is 3 years old never any problem with toileting but now the past two days she has started to poo in the bath?!! Her litter is clean , i have not started to use a different brand , she has a cat toilet which is a big size and has been great with it , it is just the past two days she has started to use the bathroom! any help appreciated..