There are many reasons to love your Oyster card. These pretty, blue, credit card-sized pieces of plastic and circuitry house a wealth of lovable convenience: you can save time buying tickets online or paying for dozens of tickets on a single top-up, save money buying cheaper tickets and of course there's the invaluable effect on one's credibility: Oysters are only useful if you live in London, so only true Londoners have Oysters. It's like a passport to the nation of London.

But my joy today in owning an Oyster lies not in any of these admirable features, but in another, less-advertised one: British rail ticket-checkers can't read them. Thus, once you're on any overland train within the zone system, your ticket is essentially free: wave your Oyster, and the sheepish guard can only shrug and take your word for it that your little blue treasure has a valid ticket buried within it. So as I travel slowly back into London on my free train ride, I say: god bless you, Oyster.