If you rent in an area covered by a selective licensing scheme, your landlord must have a licence for the property under landlord licensing rules. If they don't, they're committing a criminal offence, and you may be able to claim a rent repayment order of up to 24 months' rent through the First-tier Tribunal.
Selective licensing is different from mandatory HMO licensing, which applies nationwide to larger shared houses. Selective licensing is introduced by individual councils in specific areas where they've identified particular problems. Not every council operates a selective licensing scheme, and those that do may only cover certain streets or neighbourhoods.
To find out whether your property is in a selective licensing area, check your local council's website or contact their private sector housing team.