The leaflet (if they genuinely have been distributing leaflets) would not be soliciting in the eyes of the law.
Soliciting would be in the street, and for prosecution would need to be ‘persistently loitering or soliciting in the street’
A leaflet would be an advert, but there could be other offences depending on the content such as obscene material.
If these are being controlled by traffickers etc then it would be very idiotic to attract (and document) the extra attention by distributing leaflets in local letter boxes, and if not trafficked then it would still be extremely naive to do so, as prostitution itself is not illegal but there are offences (and prosecutions) for those managing and profiting
Leaflets would both create evidence and prompt neighbours to complain to the police / council
Even if not prosecuted for controlling prosecution councils would ultimately go towards anti social routes
The landlord may not be aware of the use, but if knowingly renting out for prostitution it could put them at risk of profiting.
They may turn a blind eye, but it’s generating problems for them in the future - other locals unhappy and future tenants getting knocks on the door
The fact that women change periodically isn’t a guarantee of trafficking, but it does indicate management of them somehow.
They could be fully willingly working and moving between locations, or they could be under control even when they apparently willingly travel
https://www.cps.gov.uk/legal-guidance/prostitution-and-exploitation-prostitution
https://www.cps.gov.uk/legal-guidance/obscene-publications#:~:text=“Obscene”%3A%20“an%20article,read%2C%20see%20or%20hear%20the
Assuming the police have visited already (as opposed to just responding to some complaints) ….. prostitution is not illegal, and unless the women are unable to work (not UK residents etc) then the issue is an anti social matter.
(The police will be identifying the ‘management’ and collating any information over the long term for potential prosecution)
If they keep themselves to themselves, and men aren’t making a nuisance then there would be little that can be done.
But men making a nuisance, explicit leafleting etc would be an issue that can be dealt with via the council
I’ve said that I find it hard to believe that they are leafleting into letterboxes.
Was it a ‘real’ printed leaflet, or could it have been printed from the internet ? That would make sense to be upfront about what’s available