Gather your medical records, appointment letters, test results, prescriptions and a clear timeline of what happened, including names of relevant healthcare providers. Note any ongoing symptoms, treatment, time off work, care needs and financial losses, keeping receipts and other supporting evidence. Record who you complained to and any responses, but avoid altering or disposing of relevant documents. A solicitor regulated by the SRA can assess whether the evidence supports a claim and explain time limits, which are often three years but can vary depending on the circumstances.