Not necessarily: an immigration lawyer is usually a solicitor or barrister, while an OISC-registered adviser may be authorised to provide immigration advice without being a lawyer. OISC is now called the Immigration Advice Authority (IAA), so check the official IAA register for the adviser’s current registration and permitted level of work. If you want a solicitor, use the Law Society’s directory and check their SRA regulation. Confirm what services are covered, the likely fees and how complaints are handled before instructing anyone.