It was certainly the same in Whitehaven where I recently lived. You rarely rarely saw the posties in trousers. Indeed, Whitehaven Man, not just the posties, can be seen wearing shorts 365 days of the year. In atrocious winter weather, I would make a point of looking out for them and one December, with snow on the ground, I did indeed spot one. Relatives tell me it’s the same in Surrey and Nottingham.
Look at the Scottish Highlands too, the guys up there invented the kilt in spite of their more severe winter weather (and midges!) We women have more sense, don’t we?!
As for the several vans, I understand the Royal Mail are big on parcel delivery now, they don’t all deliver letters.