Be careful about burden of proof with sex work, for example not knowing an escort is underage, trafficked or coerced is no defence in law.
As part of the right to rent scheme, a landlord (or their agent) has to know the names and have proof of identity of anyone living at a property over 18, they should be named on the tenancy. For minors you only have the right to know their names and D.O.B.
Most landlords are using an agency to perform these tasks and vet tenants, so you are at "arms length" in most cases. When I sign a tenancy agreement on one of my properties, I have no idea who the tenant is or what they do for a living (I only see their name(s) on the agreement), my agent takes care of everything to their professional bodies specified standard and the requirements of the law.
That may not stop something illegal from happening, but it would most likely overcome the burden of proof requirements and provide a ground for my defence if something illegal happened on my property.
This all refers to landlords who are purposely and intending to act within the law and feel morally obliged to report any illegal activity from happening on their property. A rouge landlord, is a rogue landlord and the law is unlikely to be a deterrent.
For example, a landlord was recently convicted for renting properties to an Organised Crime Group for the purposes of growing cannabis. He was clearly aware of what was going on to a significant extent, and profited from the activities. He was both the landlord and the agent.
Except the original post was about marketing to SPs deliberately and specifically as a "SP-friendly landlord". That's going to put you in a very grey area at best
If it was an SP working on her own, then that's not running a brothel and her activities would be legal. The renters status occupying the property is dealt with as above.
If the S.P. declares just herself and no minors and signs a tenancy to that effect, then you aren't involved in running or setting up a brothel.