In some cases, consent can be implied (e.g. it can be assumed that a patient has consented to abdominal palpation when voluntarily undressing and lying on couch, or when he/she offers an arm for venepuncture).
Express (oral or written) consent should be obtained for any procedure that carries material risk, and therefore, patient-specific agreement must be obtained before the procedure starts. Oral consent is valid, but it is usual to obtain written consent for major procedures. If it is only possible to obtain oral consent, it is good practice to make an entry in the patient's clinical notes to confirm advice was given and oral consent obtained, as well as the name and designation of any witnesses.