"Nick Leverton" wrote

obrail I could put a letter in the posting box on the side of any TPO
well after midnight, provided it was going in the right direction :-)
/obrail

and you'd get it postmarked with the date a day before you actually posted
it, as TPOs set their date stamps on the date when the journey began, and
didn't change them at midnight. There were occasions when a new stamp issue
came out - some people would buy the new stamps as soon as they came out at
the 24 hour post office that used to exist at Trafalgar Square, drive to
Rugby (this was soon after the M1 opened) and post letters with the new
stamps in a London-bound TPO. They would be rewarded with a 'day before
first day cover'.

Peter