You could double that number to account for the "fraud and error" spend at DWP: I would presume that further spending in this regard is dedicated to other departments.
Sure, you can fire a few low paid Jobcentre employees if you're convinced retaining that sort of admin offers no actual benefit to anyone attending, but it turns out that paying 8 million people who are neither in employment nor willing/able to ask for appointments at Jobcentres a livable income isn't cheaper