It depends. If you go into a lettings agency they will usually offer 12 month contracts (or 9 months if you are looking at student housing). If you go with a private landlord then they will draw up a contract that is specific to them. This could be for 12 months or longer, or it could be that you are not tied into any time, but need to give a certain amount of months notice before you move out. If they make you give 2 months notice then you could be living there 4 months, want to move and tell them, then have to pay 2 months rent/ live there for 2 more months before you can move on- so would end up staying 6 months.
It is worth asking the owner/ landord of the property you wish to rent and looking at ads on gumtree and so on, as well as estate agents.
Both the houses I have rented have been in Leicester (where your bio says you are from) and I have had one 9 month contract through an agency and one that was none specific, which I stayed at for 16 months.
Usually you sign a one or two year lease, but even after your lease ends you can usually rent the place for as long as you want. Most landlords are very happy to have a tenant that stays for years (assuming they are a good tenant) With the right landlord you can rent a place for 10-20 years
My guess wud b for as long as the contract says, thr shud b differant options on how long u can rent them