A councillor has a personal interest where the well-being or financial position of the councillor, members of the councillor's family, or people or bodies with whom the councillor has a close association, is likely to be affected by the business of his authority more than it would affect the majority of citizens.
A personal interest is also prejudicial if it meets all of:
a) The matter does not fall within one of the exempt categories, for example setting the council tax.
b) The matter affects the councillor's interests financially or is about a licensing, planning or other regulatory matter that might affect the councillor's interests.
c) A member of the public, who knows the relevant facts, would reasonably think the councillor's personal interest so significant that it is likely to prejudice his judgement of the public interest.
So, in the situation described, it looks as if there is a personal interest, but it may not be a prejudicial interest. A personal interest should be declared. Many councillors would regard (c) above to be sufficient to make an interest prejudicial, and would therefore withdraw from the item.