A 48-year-old woman is admitted to ICU following a large middle cerebral artery territory infarct. On day 3, she is intubated (GCS 3T), pupils are fixed and dilated bilaterally. CT shows massive cerebral oedema with complete effacement of basal cisterns. The neurology team confirms there is no prospect of meaningful recovery. The family asks about organ donation. Under UK law, what is the correct framework for determining the patient's wishes regarding organ donation?