He said if he had attended he would have been an observer and wouldn't have spoken, though there would have been difficulties if the meeting was being told information that was clearly wrong.
"I think where the society may have got it wrong was in tying the meeting to the legal action," he said. "If it had been simply a public meeting to discuss the pool issue then it would have been different."
Experts have, however, questioned the advice, including saying there were issues about councillors' rights to take part in a public forum.
Jack wrote in his email: "While attendance at the meeting might seem like an appropriate way to engage with an interest group ... the reality is that the group is in litigation against the Council, and the purpose of the meeting is to seek support for that litigation.
"It would not be appropriate for members of the Council's governing body to participate in a meeting aimed at furthering legal proceedings against the Council," he wrote.