There's not a lot I can say about this long defunct Devon cider business. In common with most of the (presumably) successful regional cidermakers which were either swallowed up or bit the dust in the latter part of the 20th century, information is rather thin on the ground.
The only bit of history I've managed to dig up on Mannings & Sons is this website for Mallard Cottage, a self-catering business on the site of the original Mannings ciderworks in Tuckenhay near Totnes. There's a nice picture of an old bottle label, but little else to flesh out the story of Mannings Vintage Devon Cider.
It's a nice jar though.