Landlord Usage of Vacated Rooms in House Share

I let out a 4 bedroom house but recently 3 of the tenants have moved out and only one tenant remains because his Termination Notice doesn't apply until July. It is a standard Part 4 tenancy. The garden area of the house is not part of the rented area and the tenants have never had access to it. Two of the ground floor bedrooms are now vacant and there is access to them via doors from the garden. I informed the remaining tenant that I want usage and access to these bedrooms and that I planned to lock the internal bedroom doors from both sides so that both his area and the bedrooms would be secure. He has objected to this request on the grounds that the electric sockets in the rooms are part of the house and that in the event of a fire or other emergency he might need access to the rooms. Currently, some appliances (Wash Machine / Dryer) are connected to sockets in these rooms although the actual appliances are located in an adjacent utility room. Any legal eagles out there have an opinion as to the legal status of the rooms assuming I connect the appliances elsewhere?