Readers might be interested in this recent Secretary of State call in decision. It involved a 41MW solar PV scheme in the AONB at Wroughton Airfield near Swindon. Permission was granted- but the interesting point for me was the consideration of the s.106 package.
The applicant had, in the s.106 unilateral undertaking, proposed a Community Trust Fund and the issue of "Solar Bonds". It was proposed that a proportion of the revenue generated from the scheme would be paid into the fund, creating an estimated £40,000 per annum for the community and that 700,000 Solar Bonds would be made available (first to local residents) at £60 at a fixed annual gross return of 6%.
The Inspector concluded, and the Secretary of State agreed, that these obligations did not fall within the scope of the 4 purposes of s.106(1) (as well as failing the CIL Reg 122 tests) and so the Secretary of State gave them no weight.
In our approach to s.106 drafting we do sometimes need to draw attention to the 4 purposes of s.106 and it is very often the case that some "obligation" are difficult to fit into the wording. But it is rare to see the point considered in a Secretary of State decision.
I am not sure, however, that the necessary conclusion in all cases is that no weight should be given simply because a covenant doesn't fall within s.106. It should depend on the circumstances. The benefit of s.106 is that covenants run with the land, but if the subject matter of the covenant is capable of being material, then there may be other circumstances which give confidence that it will be delivered even if the burden does not run with the land in the s.106 sense.