What a fantastic program! This just recently was aired in Britain, and I was afraid I might never get to see it. It's fantastic to see such a spotlight on ARCo and its engineers. The access for which was allowed for this program is quite unprecedented.
The restoration of the Spitfire Mk.I N3200 seen in the program, just like its sister restoration P9374, is extremely unique from all other Spitfire restorations (even all other Mk.I's flying today), in that they don't have any of the updates that came after early 1940. For instance, they have the Merlin III engine, bracket (two-pitch) propeller, hand-pump undercarriage, fabric ailerons, and other details that were changed on the Mk.Ia's later on in service. The other Mk.I's (and Mk.II) flying today, through cost-savings in having more accessible parts/engines, etc., are much more in common with the Spitfire Mk.V (late engines, props, later undercarriage system, etc.), than these Mk.I's, N3200 and P9374. There are over 700 design changes between the Mk.I's, as you see in N3200 and P9374, and the Mk.V. They are not "Battle of Britain" era machines, they are "Battle of France" era machines, and they are, as they were then, in more exacting detail than most would ever care to realize.
As for Guy Martin, he is a motorcycle racer with a mechanical background, who has more recently become a TV personality. He does have a keen interest in WWII aviation/history (amongst his possessions, he has a trailer-mounted ground-running Merlin XX from a Lancaster - he was, after all, named after Guy Gibson). As the program never forgets to highlight, the real restoration work was of course done by all of the talented/experienced specialists at Duxford and the Isle of White, with Guy inserted for the sake of the program, for a few days here and there.