Most UK night postal services are run by turboprops. I'm a bit out of touch with the current situation, but a number of key hubs (LPL, EMA, ???) see a wave of turboprops hubbing in and out at night.
Years ago aircraft such as Bandeirantes and Shorts 330/360's used to operate mail flights in great numbers. The Post Office then rationalised onto a smaller number of larger aircraft....Emerald 748's, Channex F27's etc.