ANYONE WHO SAW Carol Thatcher's television interview with her father last year must have been impressed by the shrewdness Denis concealed under a bufferish exterior. His friend Bill Deedes has even suggested that he welcomed his portrayal as a silly ass in Private Eye because it distracted the press from probing his influence in Downing Street. Deedes's suggestion came to mind while I was reading this new biography of P G Wodehouse.Wodehouse was old enough to be Denis's father: at first sight, that is just what he might have been. From apparently similar backgrounds, the two men shared many characteristics: dedication to sport, especially rugby; humorous self-deprecation; clear objectives in Me; belief in common sense and established standards; resolute cheerfulness and