Hi Leeroy,
The rules governing rented property are very involved.
The landlord has responsibility for many things, Gas appliances, Electrical certs, drains, roof repairs etc.
If you do not have a tenancy agreement then the Landlord could say you have no right to be in his property.
To counter this you will have evidence of the payments you have made for your rent.
If he is pressuring you to pay other peoples rent then why is he not pressuring them directly.
The Landlord can evict tenants if they break the agreement between them and the tenant; but in your case no written agreement exists. It is possible for a verbal agreement to be binding nowerdays but this would be difficult to prove.
Try the CAB for advice and get a legal agreement with your landlord.
If the landlord pressures you again about other peoples rent then consider contacting the police as this is harrassment.