A compulsory purchase order (CPO) is not generally referred to as merely "attempted" in a legal sense, but rather it goes through a four stage process where it is made, objected to, confirmed, and then executed. It is considered a last resort, and the acquiring authority must prove they have attempted to acquire the land by negotiation beforehand.
Only Brandon Estates are likely to make an objection which given the history of rejected planning and appeal only the price offered could be grounds for such an objection.
The valuation is determined by a chartered surveyor, usually appointed by the acquiring authority based on the "market value" of the land as if it were sold by a willing seller on the open market, excluding any future changes in value caused by the intended future use.