As a private tenant you have a few more options for leaving your accommodation early but you will need to check if your landlord (and flatmates) are in agreeemnt.
Break Clause
You can use a break clause if this in your contract, as it allows the tenant(s), landlord, or both, to end the tenancy early by giving notice. Ususally this is at the 6-month mark, but you should check you tenancy agreement to find out if you have this, and if so, when and how you can give notice.
If you have a joint tenancy, all tenants must give notice together to end the tenancy, unless the agreement says otherwise. This is because the break clause will end the entire tenancy, so it's not possible for just one joint tenant to use the break clause and move out whilst the others remain.
There is no requirement for a landlord to include a break clause and not all contracts have it. Usually, you will need to ask for this when negotiating the tenancy.
Assignment
This is where you find someone else who can take over your tenancy. Usually, there is a £50 fee, and you can only be charged more if the landlord shows that the change costs them more.
Your landlord (and flatmates) will need to agree to this in writing ( a ‘Deed’), but landlords usually cannot ‘unreasonably’ refuse this and having a term in your contract stating assignment is not allowed may be unfair.
It's your responsibility to find someone but if you have a letting agent, they may be able to help. You can advertise your room on Gumtree, Facebook Marketplace, or Spare Room, as well as, housing Facebook groups such as the Brunel Letting’s Flatmate Finder.
Until you find a replacement and have this agreed in writing, you will need to keep paying rent.
Subletting
This is where you find a new tenant for your room but you continue to pay rent to your landlord and the tenant pays you. Subletting can be risky, as you remain liable to your landlord for any damage caused to the property by your sub-tenant.
Usually, landlords will not agree to subletting and if you are considering this you should check with them and your flatmates before doing so.
Surrender
Lastly, this is where a landlord and tenant mutually agree to bring the tenancy to an end. This must be agreed in writing through a 'Deed'.
It is likely you will have to pay the landlord or agent ‘reasonable costs’ for a surrender.