The tension in every Mowbray house is the same: tenants want their rooms genuinely private, landlords need entry for repairs and emergencies, and both positions are legitimate. Improvised solutions serve neither — a padlock on a bedroom door gives a tenant privacy and creates a fire risk, while a landlord holding a copy of every room key gives access and destroys privacy.
A properly designed hierarchy resolves it. Each tenant holds a key that opens the front door and their own room and nothing else. The landlord or agent holds a key that opens the common parts and, where the lease permits, the room doors for lawful entry. Every room door opens from the inside without a key. It is not complicated to set up and it ends a category of disputes.
Structurally, the thing that most needs saying is about doors promoted beyond their design. When a garage or a back room was turned into a let, the builder generally reused whatever leaf was lying around and screwed the lining into board rather than into brick. An assembly like that fails at the fixings long before anything happens to the lock, so fitting a better cylinder is money aimed at the wrong component. What it needs is a lock installation done from the frame outward — solid leaf, lining anchored into masonry, and only then the ironmongery.