In Victorian times, there were several deliveries a day within the city. It was said you could be invited to a party for that night and send back your RSVP, all in the same day. When were those frequent deliveries scaled back? How many are there now?
http://www.victorianlondon.org/communications/dickens-postalregulations.htm
2 daily deliveries were the norm in urban and suburban areas until just a few years ago, certainly within the last ten years. It had been that way ever since I can remember and I am now 45 so I can just about remember the 60s. I suspect that the frequency will have declined gradually from the Victorian age as other forms of communication became commonplace, particularly the telephone.
There’s now one delivery daily, with no deliveries on Sundays or public holidays. It’s usually delivered early, in the morning, as opposed to the US where it’s often not delivered until late afternoon.
I lived in London from 1960 - 1986 and (as Blue Mood said) only remember one delivery a day, in the early morning.
There used to be telegrams, but they (and frequent deliveries) have been swept away by phone, fax and e-mail.
You can send a singing birthday card by e-mail, a signed contract by fax and have a conversation by phone. Therefore hand-deliveries of letters must be heavily down.