employers ending ssp?

Hello everyone just asking for a bit of advice please I wasn’t sure where to put this on the forum. Basically I’m signed off sick by my gp from work and getting ssp. However my employers have been dodgy with this sort of thing in the past doubting people’s genuine illness. But my question is this. If my employers for whatever reason decided to stop paying me ssp or decided to withhold my ssp from me do they have to inform me of their decision to do this or can they just do this without even speaking to me about it ? Thank you in advance.