There is only one part of this where I feel able to answer with any confidence. It is not up to the chair or the council to rule on a councillor's interest or lack of interest, nor is there any power to exclude on grounds of personal interest. It is the responsibility of each councillor to decide for themselves and face the consequences, if any.
Under the old rules, if the decision to grant a benefit (monetary or otherwise) to the trust was made by the parish council, then a councillor holding an office (such as treasurer) in the trust would be expected to declare an interest and withdraw. Under the new rules it is less clear and more likely to depend on the exact extent to which the councillor might benefit.
But where the decision is being made by another authority, the argument is even more tenuous, and the councillor could argue that the grant was in the interests of the parish as a whole and his action in supporting the application was entirely reasonable.
