Actually, and I ended up having to look this up, Mr. Bean's Mini as it is commonly know was a 1976 Mk.3. His first mini was an Orange 1969 Mk.2 that was wrecked off screen after the first series. This is trivia I did not know until now.
As a basic guideline to spotting the differences, Mk.2's still had the sliding windows; small, rounded taillights; and external door hinges from the earlier Mk.1 design. From Mk.3 on the windows were rollups; you had larger, rectangular taillights; the grill design is different (although the metalwork behind will support the earlier grills); and the hinges were concealed.
The previous owner of my Mini was aiming for that look when he painted the hood semi-gloss black even though Mr. Bean's Mini was technically yellow. This was a look I wanted to change immediately when I first bought it, but one that I'm now growing quite fond of.
And thus we conclude with my pedantic input.