I watched part 2 last night - quite funny in places, with the incompetent hitman looking for Scott in Dunstable instead of Barnstaple, and other farcical elements.. The chap playing John Le Mesurier looked and sounded nothing like him, unless it was another John Le Mesurier, which seems unlikely - most of the other actors have been made to look quite like the character they're playing. When did J Le M have a beard?
I must admit that Scott (or at any rate Scott as played by Wishaw) does become more likeable, so I retract my earlier comment.
[Edit] - apparently this John Le Mesurier was indeed a different person entirely - from the Torygraph's obituary of Thorpe: "In 1974, tasked with silencing Scott, Holmes approached a business acquaintance, John Le Mesurier (no relation of the actor) who in turn introduced him to George Deakin, a fruit machine salesman he thought would know people prepared to do the job."
