Cosby sometimes lets me on the sofa
Seriously, he lives on the sofa, lies on it during the day, sleeps on it during the night (he doesn't have a bed).
It's not a problem though, he just lies there, even if you are eating he'll just quietly sit at the other side of the sofa. If we have guests he knows he's not allowed on but he sometimes takes the huff!! There was once that he was so put out that Dave's mam was sitting in his seat that he just calmly jumped up and plonked his backside on her lap - her face was a picture
I'm not sure what he would do if I asked him to get down or told him he wasn't allowed, as theres never really been any call for us to do so - as I said he's not a pest he just sits there.
Boo on the other hand prefers the floor or his bed, but if you're sitting on the sofa he will jump up and smooch attack you - he's a bit of a pest, but he will get down if you tell him to (before jumping back up to smooch you)