Young actors dream of playing a variety of great roles, but they also fear never being offered one at all. There is, however, a third way: being famed for a single role, in one of the best-loved TV shows ever. This can bring a peculiar blend of attainment and limitation, which many performers would happily settle for. Ian Lavender, who has died aged 77, took this route with grace and patience as Private Frank Pike, the timid teenage rookie of the Walmington-on-Sea Home Guard in Dad’s Army. Lavender appeared in all 80 episodes from 1968 to 1977, and features in...