Jack William Avery (1911/1912 – 6 July 1940) was a War Reserve Constable who was murdered in Hyde Park, London, on 5 July 1940, having served less than one year with the Metropolitan Police Service. Avery was stabbed in the groin by Frank Stephen Cobbett, after Avery approached him having been advised by a member of the public that Cobbett was acting suspiciously. Cobbett, then aged 42 and of no fixed address, was originally sentenced to death for murder, but after an appeal served 15 years penal servitude for manslaughter instead.