On a protected building the rule is that nothing visible from the street changes, so security has to be added rather than substituted. Concretely: an additional bolt worked into the back of the leaf, pins set through the hanging edge so the door cannot be levered clear of its opening, and a keep bedded into the original masonry rather than screwed to a lining. Where stock justifies it, high security locks go in behind the same unchanged frontage. The shopfront looks exactly as it did and the door is in a different category.
For the trading side of that, the constraint is duty cycle. A high street premises opens for customers, deliveries and staff all day and the ironmongery has to be rated for it, which is not the same as being rated for a domestic door. Doing both — heritage-appropriate and commercially rated — is the real work here, and it is why we would rather assess a premises properly than quote from a description. Where a tenancy has just changed, that assessment usually pairs with a commercial lock change before anything else is decided.
Then there is the wildlife, which needs the opposite of strength. A troop that has learned a particular door will keep returning to it, and the fitting that stops them is one they cannot operate: a catch out of reach, a two-action release, a bin enclosure with a latch requiring a grip they do not have. On a food premises this is a trading issue rather than a curiosity, and it is worth solving properly rather than repeatedly.