Hi,
Maybe I am misreading your question, but when you say people on welfare, are you talking about someone on DSFA Rent Allowance.
Usually, the procedure is, to contact the relevant Local Authority, and fill out Application Form for same, and Register with PTRB as a landlord, and also provide a current Tax Clearence Cert. at which point, you can get all the information necessary, regarding your liability for tax.
Hope this may be of some help, and possibly someone else may be able to correct this, and offer further advice.
Best of luck with venture