There are two issues. For the MP, it is to be a question of the value of the gift. You don't ask any further questions in the current policy; it's just the value of the gift. If it's high enough, it gets publicly declared. It's up to the public or whoever's interested in these things to decide whether that's appropriate or not.
For a public office holder the matter is different because there we will try to determine whether or not there is some contact or link between the donor and something that's in the area of responsibility of that particular public office holder, and therefore whether or not it would be seen to bias that person, in which case we would say that in our judgment it's not simply enough to declare it; it's not appropriate that they should accept the gift at all.