Your Tenancy Agreement (Lease) should state any “other areas” that form part of the Lot that you're occupying (e.g. carspace, laundry). In any event, if you're sure that the laundry is part of the Lot that you are renting, then you should write to the Landlord via the Agent and advise them that, in say 7 days time:
- you intend to have the lock on the laundry door changed
- you will be seeking reimbursement of your costs (of 1) from the landlord, and that;
- if reimbursement is not made, you will be seeking Orders from the Consumer, Trader, and Tenancy Tribunal for that reimbursement and for your electricity costs covering the use of the laundry by others.
Good luck!