Question

if a councilor declares an interest in a subject can they still vote

Answer 1

It is hard to be certain exactly what rules apply in the current regime, and there is a difference between what the principles may be and the possible means of enforcement.

As best I understand it, the question depends on the nature of the interest.  If the councillor would obtain an advantage (particularly financial) for himself, his family or a close associate, then they should declare an interest and withdraw from discussion and from voting on the item.

On the other hand, a councillor may declare that an issue has some bearing on them, but not such as to give them a significant benefit, in which case they can declare the interest and continue to be involved in the matter.