Cats Keep Peeing On My Bed?

My 2 male cats are 4 years old and have been done, but since I had to move into my BF's mum's they have started peeing on the bed again. Their tray is kept clean as they get fed, watered, and sleep in the bedroom. They do it when you're in bed going to sleep. And when we are out after we cover the bed in plastic sheets they pull them off and pee. There is no UTI, as I keep an eye for that, as my female gets them now and again. Please can you help?

By Emma