Paul Clayden says in "The Parish Councillor's Guide" that "In the view of the author, there is no reason why such a committee should not include all the members of the council, if that is the wish of the council".
However, in an email Mr Clayden has subsequently qualified this by the following:
I am aware of the possible controversy about the constitution of a committee. On reflection, I think the opinion expressed by me in The Parish Councillor's Guide is not correct. A committee (in the local government context) is a body appointed by a council to perform a specified function and cannot therefore be the body itself. In practice, I doubt if any harm is caused if a council resolves itself into what it calls a committee, so long as the correct procedures are followed (giving notice of meetings etc.)