When you rent a property it is standard to take out a tenancy agreement. The most common form of these is known as an Assured Shorthold Tenancy Agreement (AST for short) and it applies to both furnished and unfurnished accommodation.
Generally, tenancy agreements are taken out to cover a specific time period, often six months but they can be for shorter or much longer periods of time. They are a legal agreement between landlord and tenant and they set out the duties and obligations of each to the other. Importantly they provide secured accommodation for the tenant, and an agreement on part of the tenant to pay rent on time and to take care of the property during the period of their tenancy.
With a six month AST the landlord can retake repossession of the property after six months, but only if he has given the tenant two months notice to vacate the property. That means that if he really wants the property back after six months, he will need to say so in writing by the end of the fourth month.
However, if the tenant is unwilling or unable to pay the due rent, or otherwise break the terms of the AST, for instance by damaging the property or upsetting the neighbours, the landlord may be interested in ending the tenancy agreement early, though again he is obliged to give two months notice.
Although tenancy agreements are generally written agreements signed by both the landlord and the tenants, legally they may also be verbal agreements. However, in most cases having just a verbal agreement is not recommended as it can become difficult to enforce should any disputes arise.
Not all ASTs are for specified time periods. Some are completely open-ended, though that too can lead to problems. Specifying a minimum time period is strongly recommended.
You can find information about different types of landlords insurance.