Goodbye to the letters of introduction

Re-reading Agatha Christie’s A Murder is Announced this week (it’s the summer holidays! I can relax like anyone else!), I was struck by one of Miss Marple’s wise pronouncements:

And that’s really the particular way the world has changed since the war. Take this place, Chipping Cleghorn, for instance. It’s very much like St Mary Mead where I live. Fifteen years ago one knew who everybody was. The Bantrys in the big house – and the Hartnells and the Price Ridleys and the Weatherbys… They were people whose fathers and mothers and grandfathers and grandmothers, or whose aunts and uncles, had lived there before them. If somebody new came to live there, they brought letters of introduction, or they’d been in the same regiment or served in the same ship as someone there already. If anybody new