Underpaid? Backbench MPs, Darling, being an MP is a vast subsidised ego trip. It's a job for which you need no qualifications, no compulsory hours of work, no performance standards. A warm room and subsidised meals for a bunch of self-opinionated windbags and busybodies who suddenly find people taking them seriously because they got letters "MP" after their names. How can they be underpaid when there're about two hundred applicants for every vacancy? You could fill every seat twenty times over even if they have to pay to do the job.
It is not for a humble mortal such as I to speculate on the complex and elevated deliberations of the mighty. But in general, I think Sir Frank believes that if the Treasury knows something has to be done, the Cabinet shouldn't have too much time to think about it.