In this case, there would only be person who was eligible to vote, which would mean the committee or council would not be quorate. Therefore, if it were a committee it should be referred to full council. If this is was full council, then they should have declared their interests and then acted in the public interest (not their own), but again, there is an exception to interests if doing so would make the council non-quorate.
The councillors have 28 days to declare their interest if they haven't already done so.
When / If they fail to declare it, you can refer it to the monitoring officer for investigation.