I'm a private landlord, and am also qualified property lawyer. It does all depend on the type of tenancy agreement which you have signed. Generally they are Assured Shorthold Tenancy Agreements, and include a clause which states that the Landlord must give you at least 24 hours notice prior to himself or an agent of the landlord (i.e. plumber) entering the property. Some ASTAs also require notice in writing. But as someone else said, if there is an emergency then they can enter.