REducing With MetfOrmin Vascular Adverse Lesions in Type 1 Diabetes (REMOVAL)

Inclusion Criteria: * Type 1 Diabetes for five years or more\* * Age 40 years or above * 7.0 =\< HbA1c \<10.0% (53 - 86 mmol/mol) AND 3 or more of the following ten CardioVascular Disease (CVD) risk factors: * BMI \>27 kg/m\^2 * Current HbA1c \>8.0% (64 mmol/mol) * Known CVD/peripheral vascular disease * Current smoker * Estimated glomerular filtration rate (eGFR) \<90 ml/min per 1.73 m\^3 * Confirmed micro- or macroalbuminuria \[according to local assays and reference ranges\] * Hypertension (BP \>=140/90 millimeters of mercury (mmHg) or established on antihypertensive treatment) * Dyslipidaemia \[total cholesterol \>=5.0 mmol/L (200 mg/dL);OR HDL cholesterol \<1.20 mmol/L (46mg/dL) \[MEN\]; OR \<1.30 mmol/L (50 mg/dL) \[WOMEN\]; or triglycerides \>=1.7 mmol/L (150mg/dL); or established on lipid-lowering treatment)\] * Strong family history of CVD (at least one parent, biological aunt/ uncle, or sibling with myocardial infarction or stroke aged \<60 years) * Duration of diabetes \> 20 years Exclusion Criteria: * eGFR \< 45 ml/min/1.73m2 * woman of childbearing age not on effective contraception * Pregnancy and/or lactation * Acute coronary syndrome or Stroke/Transient Ischaemic Attack within the last three months * NYHA stage 3 or 4 heart failure * Significant hypoglycaemia unawareness * Impaired cognitive function/ unable to give informed consent * Previous carotid surgery/ inability to capture adequate carotid images * Estimated glomerular filtration \< 45ml/min/1.73m\^2 (MDRD) * Gastroparesis * History of lactic acidosis * Other contraindications to metformin (hepatic impairment, known hypersensitivity to metformin, acute illness such as dehydration, severe infection, shock, acute cardiac failure or suspected tissue hypoxia) * Any coexistent life threatening condition including prior diagnosis of cancer within two years * History of alcohol problem or drug abuse