THE DEATH penalty is an interesting crux for our democratic society. MPs overwhelmingly oppose it and yet, 50 years on from the last hangings in Britain, a slight majority of those who elect them would like to bring it back.This week ITV marked that anniversary with a documentary called Executed ­(12 August), which looked at the final ­executions: two criminals, participants in the same murder, died at the same time, 30 miles apart. The programme also revealed the mechanics of hanging, a medieval technology designed to kill slowly and painfully by strangulation, redesigned to kill quickly and painlessly by fracture. It was not 100 per cent successful in either.Most of the programme, though, was devoted to the three miscarriages of justice that led to a widespread outcry and street