Yup. Wreck his reputation, and it would violate his contract and might be liable to damages. I mean, do you want to be known as an unethical wanker in your professional circles?
20M sounds about right. I'd not budge one single centimeter either. He can create the greatest Garden ever seen in the green and pleasant land of England.
Not sure one of those was his fault. If you believe they were then 4 is fair. 5 or 6 for me. He wasn't exactly brilliant but if you slip, not much you can do.