I have enjoyed reading this recently published book. Andrew Gimson, who previously wrote on kings and queens, gets this about right going through the list giving you his assesment and the salient facts with surefootedness. I found there were some PMs who I know of because they have served in my own life time (Wilson, Heath, Blair, etc) others I know from the history books (Gladstone, Disraeli, Attlee, etc). Some I had heard of but knew little about (Walpole, Balfour, MacDonald, etc) others I had practically never heard of (Henry, Pelham, the Earl of Aberdeen, etc). I was interested to read of the evangelical convictions of Spencer Perceval, of which I was not aware. It is surprising to see how much the parties have changed down the years. Martin Rowson's cartoon portraits are a little hit or miss. They add to the attractiveness of the book.
Bonhoeffer uses a similar phrase 'worldly Christianity'. It's J Gresham Machen that I want to line up most closely with. See his Christianity and culture here. Having done commentaries on Proverbs (Heavenly Wisdom) and Song of Songs (Heavenly Love), a matching title for Ecclesiastes would be Heavenly Worldliness. For my stance on worldliness, see 3 posts here.