Ok "SHOULD" was probably the wrong word hobbit. You cannot deny that it is best practice to talk to an ANSP or use a listening squawk if near their airspace - especially Solent as the layout is fairly confusing if you are not used to flying around it. I do understand that you don't have to but why wouldn't you?! All it takes is a slight navigation error and you have infringed -wouldn't you rather have eyes on the ground looking out for you? Same as if you have an emergency, it's better to be talking to someone.
Non radio aircraft outside CAS don't, and can't, talk to anyone, and probably wouldn't wish to anyway.