I haven't rented since 2018, so am not familiar with the current law, but surely they can review the rent on renewal, which for most of my tenancies happened every six months (renewal, not rent rise).
My sister's rent went up last year 'Because of Covid', and the year before 'Because of Brexit'. Personally I think it was just 'Because of Greedy Landlord' but she accepted the increase as she's got two kids, the house suits them, it's near their school, near my mum, and she didn't want the hassle of moving.