Inclusion Criteria:

          1. Oropharyngeal squamous cell carcinoma (OPSCC) in base of tongue and tonsil with a
             Multidisciplinary Team (MDT) recommendation for treatment with definitive concurrent
             chemoradiotherapy

          2. All OPC T4 or N3 (HPV+ and HPV-) OR all HPV -ve (negative) OPC T1-T4, N1-N3 or T3-4,
             N0 OR HPV +ve (positive) OPC T1-T4 with N2b-N3 nodes AND who are smokers ≥ 10 pack
             years current or previous smoking history

          3. Minimum life expectancy of 3 months

          4. Eastern Cooperative Oncology Group (ECOG) performance status 0-1

          5. Adequate renal function, glomerular filtration rate (GFR) >50ml/min calculated using
             Cockcroft-Gault formula

          6. Adequate bone marrow function (absolute neutrophil count (ANC) ≥1.5 x 109/L,
             haemoglobin ≥9.0g/dL and platelets ≥100 x 109/L)

          7. Adequate liver function i.e. plasma bilirubin ≤1.5 times the upper limit of normal
             (ULN), and alanine aminotransferase (ALT) and alkaline phosphatase (ALP) ≤2.5 x ULN

          8. Prothrombin time (PT) ≤1.5 x ULN or International Normalised Ratio (INR) ≤1. 5

          9. Magnesium ≥ lower limit of normal

         10. No cancers in previous 5 years, except basal cell carcinoma of skin and cervical
             intra-epithelial neoplasia (CIN)

         11. Aged 18-70

         12. Written informed consent given for the trial

         13. Surgically resectable disease if being randomised to all four arms

         14. Females must either be of non-reproductive potential (i.e. post-menopausal by history:
             ≥55 years old and no menses for ≥1 year without an alternative medical cause; or
             history of hysterectomy, or history of bilateral tubal ligation or history of
             bilateral oophorectomy) or must have a negative serum pregnancy test upon study entry

         15. Willingness to comply with the protocol for the duration of the study, including
             undergoing treatment and scheduled visits and examinations including follow up

        Exclusion Criteria:

          1. All T1-T2,N0 OPC (HPV +ve or HPV-ve)

          2. HPV positive patients who are:

             T1-T3, N0-N2c non-smokers T1-T3, N0-N2c smokers with ≤10 pack years or T1-T2, N0-N2a
             smokers with ≥10 pack years

          3. Unfit for chemoradiotherapy regimens

          4. Creatinine Clearance <50ml/min

          5. Treatment with any of the following, prior to randomisation:

               1. Any Investigational Medicinal Products (IMP) within 30 days

               2. Any other chemotherapy, immunotherapy or anticancer agents within 3 weeks

               3. Major surgery within 4 weeks

          6. History of allergic reactions to any of the IMPs and excipients used in this trial

          7. Uncontrolled intercurrent illness including, but not limited to, ongoing or active
             infection, symptomatic congestive heart failure, uncontrolled hypertension, unstable
             angina pectoris, cardiac arrhythmia, active peptic ulcer disease or gastritis, active
             bleeding diatheses including any subject known to have evidence of acute or chronic
             hepatitis B, hepatitis C, Human Immunodeficiency Virus (HIV), or psychiatric
             illness/social situations that would limit compliance with study requirements or
             compromise the ability of the subject to give written informed consent

          8. Women who are pregnant or breast-feeding. Women of child- bearing potential must have
             a negative pregnancy test performed within 7 days prior to randomisation

          9. Men or women who are not prepared to practise methods of contraception of proven
             efficacy during treatment and for 6 months following the end of treatment

         10. Any condition that, in the opinion of the Investigator, would interfere with
             evaluation of study treatment or interpretation of patient safety or study results

             Additional Exclusion Criteria for Arm 5 only:

         11. Any previous treatment with PD-L or PD-L1 inhibitor, including durvalumab

         12. Current or prior use of immunosuppressive medication within 14 days before the first
             dose of durvalumab, with the exceptions of intranasal and inhaled corticosteroids or
             systemic corticosteroids at physiological doses, which are not to exceed 10 mg/day of
             prednisone, or an equivalent corticosteroid dose

         13. Active or prior documented autoimmune or inflammatory disorders including inflammatory
             bowel disease e.g. colitis or Crohn's disease, diverticulitis (with the exception of
             diverticulosis), celiac disease, systemic lupus erythematosus, Sarcoidosis syndrome,
             or Wegener syndrome (granulomatosis with polyangiitis, Graves' disease, rheumatoid
             arthritis, hypophysitis, uveitis). The following are exceptions to this criterion:

               -  Patients with vitiligo or alopecia

               -  Patients with hypothyroidism (e.g. following Hashimoto syndrome) stable on
                  hormone replacement

               -  Any chronic skin condition that does not require systemic therapy

               -  Patients without active disease in the last 5 years may be included but only
                  after consultation with the study physician

         14. Patients with an active non-infectious pneumonitis

         15. History of primary immunodeficiency

         16. History of allogeneic organ transplant

         17. Known history of previous clinical diagnosis of tuberculosis

         18. Receipt of live attenuated vaccination within 30 days prior to study entry or within
             30 days of receiving durvalumab. Inactivated viruses, such as those in the influenza
             vaccine, are permitted