Green’s Dictionary of Slang

bobby-dazzler n.2

[bobby n.1 (1) + SE dazzler]

(UK Und.) a cosh, pres. used against the police.

[UK]Leeds Times 9 May 6/4: My husband [...] took a life preserver, or as he generally calls it, a ‘bobby-dazzler’, and struck the scientific mesmerist a blow over the sconce.