Working groups are temporarily set up either by a committee or the council with specific tasks stated as to what they are expected to carry out on behalf of the committee or council. They are not formed to make decisions on behalf of the PC. They are not bound by normal requirements ( notice of meeting, minute taking, open to public) Members of the public who serve on a working group should be treated as if they were members of the council and as such should be in receipt of all information required to carry out the task of the working group.
It would be strange that a working group would need to have a confidential section anyway as members should be bound professionally by confidentiality in all they do as a matter of course as they are preparing information for the PC to make decisions on.