What to do if you have separate tenancies and the landlord is trying to move a new tenant in
Government guidelines state that “home buyers and renters should, where possible, delay moving to a new house while measures are in place to fight coronavirus." However, the guidelines are merely advisory.
If you don't want your landlord to move a new tenant in, your best option is to try and negotiate with the landlord. The landlord may be able to change the start date to move the new tenant in once the restrictions are lifted and the risk to your household is lower. The new tenant may also prefer to delay the move.
If you can't delay the move, follow social distancing measures with your new housemate as closely as you can.