Our sofa is erm...well loved. 2 dc and a dog have left it looking pretty grubby but it's comfy and huge and to replace it would be ££££.
The covers are removable and according to the label are 83% polyester and 17% cotton. Sponge clean only. Would I be crazy to throw one in the washing machine on a very gentle cycle and see how it comes out? My other option is hiring one of those rug doctor things and attacking it with the upholstery tool.