I think the best (worst) experience I had with the British postal system was, a few years ago now, Lyn and myself were on holiday in Majorca, arrived on the Sat. Sent step daughter a card on the following Wed. It was posted at lunchtime, it had a postmark on it saying Palma at 6:30pm the same day, 800 miles later it had a London postmark on it saying 1:00pm the following day, from London to Amersham, where we live, 25 miles, it took 2 weeks, we were home before the card arrived, great British postal service.
Cheers
Pete.