Inclusion Criteria

          1. Histologically confirmed recurrent or metastatic squamous cell carcinoma of the head
             and neck that is considered incurable by local therapies.

          2. Measurable disease evaluated by RECIST v1.1

          3. WHO performance status of 2

          4. Life expectancy of at least 12 weeks

          5. Aged ≥ 18 years of age

          6. Adequate Bone marrow function:

               -  Absolute neutrophils grade 0 or 1 (using CTCAE v5)

               -  Platelets grade 0 or 1

               -  Haemoglobin grade 0 or 1

          7. Adequate renal function:

             Creatinine grade 0 or 1 Calculated glomerular filtration rate (GFR) ≥ 50 mL/min
             estimated using validated creatinine clearance calculation (e.g. Cockcroft-Gault or
             Wright formula). If calculated GFR is < 50 mL/min then an isotope GFR assessment
             (Cr51-EDTA or 99mTc-DTPA) should be performed. If an isotope GFR test is unavailable
             an estimation from 24 hour urine collection may be used

          8. Adequate liver function:

             Serum bilirubin grade 0 or 1 AST and ALT grade 0 or 1 (up to grade 2 for patients with
             liver metastases)

          9. Willing to use contraception for the duration of trial treatment and for 120 days
             after completion of treatment

         10. Willing to have a new biopsy, if site of disease is accessible and considered safe to
             biopsy by investigator If newly obtained samples cannot be obtained (e.g. inaccessible
             disease or patient safety concern) sites may submit archival tissue only upon
             agreement from the sponsor

         11. Able to give informed consent, indicating that the patient has been informed of and
             understands the experimental nature of the study, possible risks and benefits, trial
             procedures, and alternative options

         12. Willing and able to comply with the protocol for the duration of the study, including
             the treatment plan, investigations required and follow up visits

        Exclusion Criteria:

          1. Patients with undifferentiated nasopharyngeal or sino-nasal cancers

          2. Disease suitable for treatment with curative intent

          3. Prior therapy with an anti-PD-1, anti-PD-L1 or anti-PD-L2 agent

          4. Any investigational agents within 4 weeks prior to registration

          5. Anti-cancer monoclonal antibody therapy within 4 weeks prior to registration

          6. Chemotherapy, targeted small molecule therapy, or radiotherapy within 2 weeks prior to
             registration

          7. Patients with concurrent or previous malignancy that could compromise assessment of
             the primary or secondary endpoints of the trial

          8. Is pregnant or breastfeeding, or expecting to conceive or father children within the
             projected duration of the trial, starting with the pre-screening or screening visit
             through 120 days after the last dose of trial treatment

          9. Grade 3 or 4 peripheral neuropathy

         10. Any serious and/or unstable pre-existing medical, psychiatric or other condition that,
             in the treating clinician's judgment, could interfere with patient safety or obtaining
             informed consent

         11. Active central nervous system (CNS) metastases and/or carcinomatous meningitis;
             subjects with previously treated brain metastases may participate provided they:

             Are stable, without evidence of progression for at least four weeks prior to the first
             dose of trial treatment Have no evidence of new or enlarging brain metastases Have no
             evidence of leptomeningeal disease Are not using steroids for at least 7 days prior to
             trial treatment

         12. Has a known history of or is positive for hepatitis B (hepatitis B surface antigen
             [HBsAg] reactive) or hepatitis C (hepatitis C virus [HCV] RNA [qualitative] is
             detected) NB: Without known history, testing is required to determine eligibility.
             Hepatitis C antibody testing is allowed for screening purposes in sites where HCV RNA
             is not part of standard of care

         13. Immunocompromised patients (e.g. known HIV positive status)*

         14. Prior organ transplantation including allogenic stem-cell transplantation

         15. Has a history of (non-infectious) pneumonitis that required steroids, or current
             pneumonitis

         16. Active infection requiring systemic therapy

         17. Has received a live vaccine within 30 days prior to registration (seasonal flu
             vaccines that do not contain live virus are permitted)

         18. Has a diagnosis of immunodeficiency or is receiving systemic steroid therapy or any
             other form of immunosuppressive therapy within 7 days prior to the first dose of trial
             treatment (NB: the use of physiologic doses of corticosteroids may be approved after
             consultation with UCL CTC)

         19. Active autoimmune disease that might deteriorate when receiving an immune-stimulatory
             agent. Patients with the following are eligible:

             Autoimmune-related hyperthyroidism or autoimmune-related hypothyroidism who are in
             remission or on a stable dose of thyroid-replacement hormone Vitiligo Psoriasis

         20. Current use of immunosuppressive medication, except for the following:

        intranasal, inhaled, topical steroids, or local steroid injection (e.g., intra-articular
        injection) Systemic corticosteroids at physiologic doses ≤ 10 mg/day of prednisolone or
        equivalent (after approval by UCL CTC) Steroids as premedication for hypersensitivity
        reactions (e.g., CT scan premedication)

        *Testing for HIV for the POPPY trial is not mandatory, however if this test has been done
        the result should be known prior to registration.