It depends on the cancellation clause in your agreement. If there is no such clause, the only way you can end your lease early without being in breach of contract is if your landlord agrees to it or if your landlord is in material breach of the lease (for example, by failing to maintain the outside of the property, as agreed in the contract, and this makes it impossible for you to remain on the property. But you will have to prove this, though).
You can still end the lease early in terms of the Consumer Protection Act [68 0f 2008]. Section 14 allows for the tenant to prematurely cancel a fixed lease [by given 20 business days notice] however it should be noted that the landlord may impose a reasonable cancellation penalty . It should be noted that this penalty amount should not be to punish the tenant but reflect reasonable costs in securing a replacement tenant.