Increasing your rent
If your contract has a procedure for increasing rent then your landlord must follow it. In a fixed-term tenancy agreement (i.e. a six month or one year contract), your landlord can only put the rent up at the end of the fixed term, and you are allowed to try and negotiate the amount. You can reject the rent increase and your tenancy will continue at the original rent on a rolling, month-to-month contract, though this may mean that your landlord begins eviction proceedings against you.
If your contract is a rolling month-on-month/week-on-week tenancy, your landlord can only increase the rent once a year, and they can only do so via what is called a section 13 notice. The notice must be served on the government’s ‘form 4’, ‘Landlord’s Notice proposing a new rent under an Assured Periodic Tenancy of premises situated in England’. The increase can only take effect after a reasonable period of time - usually one month for a rolling tenancy.
You can challenge rent increases via the government’s tribunal system (https://www.gov.uk/housing-tribunals), though again, your landlord may simply choose to begin eviction proceedings against you at this point.