Assured shorthold tenancy
If the tenancy started after February 1997 it will almost certainly be an 'assured shorthold' tenancy. Most landlords choose this type of agreement for new tenancies, because it gives you a fairly straightforward way of getting the property back when you want it - although the lack of security can put off tenants who want to put down permanent roots. And tenants without much security may be more likely to leave without giving proper notice.
The agreement usually runs for a specific time - called a 'fixed term' - usually six or twelve months. The agreement will probably say that the tenant is responsible for paying the rent right up to the end of that fixed term, even if they leave before. If you want a tenant to leave at the end of the fixed term, you must give them notice in writing at least two months earlier. But you don't need a reason for doing this. Find out more about ending a tenancy at Gov.uk.