[cstross]

Those landlords are breaking the law (and the terms of your tenancy) and I believe you can file a report with the police that will get them into very hot water with their local council -- potentially fined and booted off the register of landlords (which means it'd be an offense for them to let any flats out at all).

Source: my sister is a landlord.

[lambada]

And then after doing that you're left without a flat and have to find yet another one, with another landlord or agency who will likely do exactly the same

[eterm]

England doesn't have a register of landlords, anyone can let out property.

[semanticist]

Scotland does: https://www.landlordregistrationscotland.gov.uk