For what it’s worth, this helped us understand:

Faraday Development Ltd v West Berkshire Council: Court of Appeal gives important guidance on development agreements and options, and declares contract ineffective

The Court of Appeal decided that… (see item 4)

However, entry into the development agreement was still unlawful, because looking at the substance of the arrangements taken as a whole, they involved the Council in committing itself to the procurement of works from the developer – if the developer did draw down the land, a public works contract would come into being, and it would then be too late to carry out the required procurement. This was both a breach of the Public Contracts Regulations (actual or anticipatory), and a breach of public law (because it involved the Council in effect agreeing to act unlawfully in the future).

And what is UNLAWFUL?

That which is contrary to law. “Unlawful” and “illegal” are frequently used as synonymous terms, but, in the proper sense of the word, “unlawful,” as applied to promises, agreements, considerations, and the like, denotes that they are ineffectual in law because they involve acts which, although not illegal, i.e. positively forbidden, are disapproved of by the law, and are therefore not recognized as the ground of legal rights, either because they are immoral or because they are against public policy.