Lunchtime. Parked beside the window in the Covent Garden branch of a well-known café chain, drinking horrible tea just so I can escape the rain and absorbed in the last few chapters of Possession, I'm startled by a salvo of banging at my left ear. There is a woman, about sixty, resplendent in fuchsia Pac-A-Mac and bifocals, standing on the pavement and smacking her fist against the glass. Another woman is standing next to her, sensible in black Marks coat, looking apologetic. Oh God. Is this a surprisingly middle-class central London crazy? Or a kindly maternal type alerting me to some sort of skirt-in-knickers shame? Neither, I realise, as she stabs a finger in the direction of my book's cover and then waggles a thumbs-up sign, grinning manically. It seems that AS Byatt's Booker winner stirs up as strong emotions offline as it does on the Guardian books blog.
Novels aren't just sources of solitary cogitation. They are social objects, and we use them to brandish our identities, mark our allegiances and broker our relationships. They can provoke passions as strongly as politics. Thanks to the intimate connection between story and reader, they impact upon us very personally, and can drive otherwise undemonstrative folk to feel they have a right – nay duty – to confront complete strangers with their zeal, and have thus been responsible for some of the most unexpected human encounters I've had.