Stop trusting Google Maps blindly. It is often wrong about M&S Dunfermline. I have seen it say “Open 24 hours” before. Who is kidding who?
The only reliable source is the official M&S website’s store finder. Type in “Dunfermline,” and check the pop-up that appears. That little box is your bible for the day.
Alternatively, just call them. It feels old school, but a 30-second phone call saves you a 15-minute drive of disappointment. (And saves you from the same pitying shrug I got from the security guard.)