I'm certainly not defending it, but these clauses can also be found in UK rental contracts made by estate agents. The clause will usually state that if you continue in the house after the term of the contract without renewing through the agency (and paying their exorbitant annual fees again) they will charge you a "finders fee" on the basis that you found the landlord through them originally. No idea on the legality…
Landlord letting fees banned in Wales to help tenants https://www.bbc.co.uk/news/uk-wales-politics-49542333