Inclusion Criteria:  Consenting adult female patients (≥18 years, <80 years) undergoing mastectomy or breast conserving surgery for the primary excision of confirmed or suspected breast cancer under general anaesthesia (including those with simultaneous insertion of tissue expanders or implants). American Society of Anaesthesiologist (ASA) physical scale 1-3  Exclusion Criteria:  Pre-existing pain at site of surgery, axilla, ipsilateral side of chest wall or the ipsilateral upper arm Re-excision procedures where the margins at the index surgery have been deemed insufficient When immediate autologous reconstruction surgery is planned Where delayed autologous reconstruction surgery on the operative breast within one year is planned or deemed likely Planned use of regional analgesia infusions Inability to communicate in English Impaired cognition Pregnant or lactating females Known metastatic disease Sensitivity or known contraindication to lidocaine (or other amide local anaesthetic agents e.g. other amide local anaesthetic agents: ropivacaine, bupivacaine, mepivacaine, prilocaine, etidocaine), including patients with porphyria or methaemoglobinaemia History of epilepsy Baseline heart rate < 50 bpm or systolic blood pressure < 100mmHg. Acute coronary event in the last three months Cardiac conduction abnormalities, including; Heart block (all degrees), Bundle Branch Block or Fascicular block, Prolonged QT interval, Wolf Parkinson White syndrome, channelopathy such as Brugada syndrome. A preoperative Electrocardiogram (ECG) is not mandatory. Abnormal serum potassium concentration (based upon site laboratory reference ranges) Abnormal serum sodium concentration (based upon site laboratory reference ranges) Active liver disease e.g. viral hepatitis, alcoholic liver disease, non-alcoholic fatty liver disease, haemochromatosis, other rarer causes) Abnormal liver function tests (based upon site laboratory reference ranges) Medications within the last 7 days which are known / suspected to slow lidocaine metabolism (amiodarone, beta blockers, cimetidine, fluoroquinolones, fluvoxamine, imidazoles, macrolides, verapamil, HIV drugs) Cardiac Failure Severe Renal Failure (Creatinine Clearance of less than 30ml/min or dialysis dependent)