During the roof rescue scene, the sky changes back and forth from bright and sunny to completely overcast in a matter of seconds.
During the roof rescue scene, Martin calls Mr. Coley "Mr. Creley", "Mr. Maynard", and "Mr. Munsen" because he didn't really care about the name of Mr. Coley. It is not a character error, but rather directly in character with Dr. Ellingham.
When Doc Martin goes up the ladder, he reaches the top and the clock tower wobbles when he gets off the ladder.
Maggie heads the wrong way as she leaves Joe walking to see the Doc (4:45 min). She's shown heading toward an old hotel on a dead end road, (as revealed by Google Maps). Filmed in the adjacent port (Gaverne), she should have headed the other way, (West) on the Port Gaverne Road to Port Isaac (Port Wenn).