I disagree. The government should take decisions based on the lifetime value- including trying to quantify the nature value of the alternatives and the implied costs of financing- and then make the best decision. Not the one that gives them the best bang for the buck in a moment, or a 5 year term. A lot of the issues with the current state of uk public finances are a product of short term decision making. I understand that the political system disincentivises long term decision making, and that its difficult to quantify things like nature value. But they should always strive to make that decision:
Lifetime value of alternative = present value of infrastructure + future value added from nature benefits - present value of cost (including maintenance, financing costs, opportunity cost of funds)
Whichever is the greater should be the winner and they should show their workings and lets be honest about it.