Half the fun of an early morning chat-fest lies in seeing how the presenter will handle the guests. What if they don’t get on? What if they turn out to be such badly assorted specimens of modern humanity that no common ground exists? Libby Purves, long-time adornment of Midweek, is, it should straightaway be said, a very superior compère: enthusiastic, well-briefed, never afraid to get down to brass tacks, but occasionally allowing a faint hint of steeliness to inform her interview technique; keen for fun to be had, but giving the impression that she wouldn’t stand any nonsense if the chips were down.A less experienced helmswoman, placed in a studio with the actress Pam St Clement, the ocean swimmer Adam Walker, the concert pianist Sam Haywood and John Sutherland and hi