I am not a lawyer and have no experience of this situation but here's my tuppence worth. I am more concerned with safety than the garden as this situation could have a tragic outcome in the event of a fire.
I would ask Scotland Fire and Recue Service for a fire safety visit. You fill in the form online and they'll reply.
The Fire Safety (Scotland) Regulations 2006 and the Building Standards Technical Handbook 2022 outline the requirements for fire escape routes and exits.
They can be locked however the locking devices on final exit doors and escape windows should not prevent occupants from escaping. Locks should be designed to allow easy and immediate release in an emergency.
If any of the flats are HMOs these are licensed and have very clear rules. In Scotland, Houses in Multiple Occupation (HMOs) must adhere to fire safety regulations outlined in Part 3 of the Fire (Scotland) Act 2005
Fire Door Checks:
- Quarterly checks on fire doors in common areas and annual checks on fire doors at the entrances of individual tenant dwellings are necessary.
With no residents having a key to access to the fire escape (except perhaps this man) a new, approved lock should be fitted as a matter of urgency.
This blocked fire escape should be reported to the HMO licensing department (If there is an HMO for any flats). If the escape route through the main entrance was blocked by fire or debris, the residents would have no means of escape. This would be of greater concern to me than garden or cellar access.
Him locking the doors to the cellar and communal garden for sole use may not present a risk for other residents but it deprives them of the benefit of communal areas. Do your deeds refer to a drying green or specific use for the garden. What did it look like when you bought 5 years ago? Do you still have the listing or any photos? Can you look on Google maps to see historic images to see when it was altered to an allotment? Not all years are photographed but it could give a timeline.
Do you have legal cover with your insurance? If so, contact them for advice. If not, look for a lawyer specialising in property disputes and gather copies of communication/documents, deeds, photographs and arrange an initial consultation.
The lack of regard for the safety of the residents is alarming. Maintaining an escape route is essential and a legal responsibility for all landlords, not just HMO residences. The properties that are rented must meet safety standards and the students in this tenement deserve better.
Over the 5 years of letting, did your agency not do inspections or did you carry them out? These records would show when he locked the fire door and what remedial action was taken.