The People of the Ruins

"Trapped in a London laboratory during a worker uprising in 1924, ex-artillery officer and physics instructor Jeremy Tuft awakens 150 years later - on the eve of a new Dark Age! England has become a neo-medieval society whose inhabitants have forgotten how to build or operate machinery. Though he is at first disconcerted by the failure of his own era's smug doctrine of Progress, Tuft eventually decides that post-civilized life is simpler, more peaceful. That is, until northern English and Welsh tribes invade- at which point Tuft sets about reinventing weapons of mass destruction"--