If the land is presently 'agricultural' which has quite a narrow definition......and becomes 'other than that', the council could be shooting themselves in the foot. If they absorb it out of 'agricultural' they have already removed, by their own actions, a safeguard; the owner can then argue that he would like to build several houses on this land (other restrictions notwithstanding) and the Planning Department cannot then refuse these proposals using the fact that the land is 'Agricultural'.
I imagine that your Local Authority, either (a) can't be bothered expending the time, or (b) can't be bothered spending the money, on establishing *who* owns the land, or the implications for them and the land, if they were to take it over.
I have a feeling that someone somewhere is going to need to put their hand in their pocket to determine the legality of *all* the proposals.