Start with Citizens Advice or Shelter for practical guidance on your rights and possible next steps. Your local council’s housing team may be able to investigate serious hazards, harassment or illegal eviction, and should advise you if you are at risk of homelessness. For unresolved complaints, you may be able to use the Housing Ombudsman for social housing or a government-approved redress scheme for a letting agent; arrangements differ across the UK. If court action or eviction is involved, consider getting advice from a solicitor regulated by the SRA or another appropriate legal advice service.