John Walsh: I'd rather not have all these followers

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At the end of the new Tate Modern exhibition, Exposed: Voyeurism, Surveillance and the Camera, there are some startling pictures of suffragettes. Startling because they were secretly taken photographs, snapping the women so they could be identified if they took future action against public order.

At the end of the new Tate Modern exhibition, Exposed: Voyeurism, Surveillance and the Camera, there are some startling pictures of suffragettes. Startling because they were secretly taken photographs, snapping the women so they could be identified if they took future action against public order.

Even in 1913, the authorities were peeping and prying and spying on people. A century later, we're the most surveyed – or surveillanced – nation in the world, with CCTV, speed cameras, webcams, Google satellite inspections. We can't take our privacy for granted anymore. As the Boomtown Rats rhythmically averred, there is always someone lookin' at ya.

But the "someone" is always deemed to be the bad guys in power, isn't it? The Home Office, the police, the courts, the military-industrial complex. They're the ones invading your life and grassing you up to the speed police, the clampers, the law. What, though, if we found that our privacy was being eroded by ourselves? If your identity can be stolen on Facebook, can your privacy be invaded by Twitter?

An actor friend told me his experience the other day. He – let us call him Andy – appears in a famous comedy show and is easily recognisable. On the day in question he travelled from Brighton to London, caught the Tube to BBC TV centre, lunched in Shepherd's Bush, returned to the studio, knocked off at 6.30, split a bottle of wine with his producer, caught the Tube, then the train home to Brighton.

On that train, he was approached by a stranger who said, hardly able to speak through guffaws, "I know everything you've been doing today." He proceeded to list every location Andy had visited, where he'd worked, lunched and drank. It had started when a Twitterer announced to his followers that Andy was sitting beside him on a train due to arrive in London at 11.40. As Andy walked on the concourse, he was being watched, and tweeted about. Further reports monitored his Tube ride, his walk down the BBC corridors, his lunch date. The laughing idiot on the train even showed him a list of Twitter feeds that charted his progress on his iPhone.

Perhaps it's a harmless development of fandom that can see a citizen being stalked and spied on like this. But if one thinks of John Lennon and his most famous fan, the phenomenon of the Twitter-stalk doesn't seem quite so harmless, does it?

The day I saw both sides of the Hopper legend

I had the pleasure of meeting Dennis Hopper once, at Amsterdam's Stedelijk Museum in March 2001. It was hosting a "retrospective" of his artworks – though very few of them had been exhibited anywhere before, or been bought by anyone (though many had been given away to friends). The exhibits were bewilderingly eclectic – huge Pop Art, Lichtenstein-ish billboards, abstract expressionist drip-paintings, objets trouvés, home movies and installations, including a neon scribble saying "This is Art," that was done years before Tracey Emin started making neon scribbles her calling card.

I remember how weirdly healthy looking Hopper was at 64, how compact, neatly bearded, fit and genial, as he worked the room, matily grappling with friends, slapping shoulders, exchanging banter with his pal Julian Schnabel. He seemed a long way from the swivel-eyed, perma-stoned, gun-toting tyrant of legend. I remember being shocked by his airy claim that it was he who invented conceptual art in California in 1962 with a light-show installation called Proof.

But I most vividly recall what happened when, over breakfast the morning after the exhibition, we talked about Easy Rider and its difficult genesis. How Hopper had gone to New Orleans and Texas to find movie locations and accommodation for the crew, leaving Peter Fonda and Terry Southern in LA to work on the screenplay.

"I got back and called them and said, 'How's the script going?' And they said, 'Oh we haven't really written anything,'" said Hopper, eyes starting to blaze, voice rising to a yell. "So I went over and they were having a big fucking DINNER PARTY, and I walked in and said, 'You fucking ASSHOLES, sitting here while I can't even go through TEXAS because they're cutting longhairs with a rusty RAZOR BLADE...'" There followed a complex tale about which man pulled a knife on whom – but I couldn't follow. I was too drenched with fear as the smiling, senatorial, arty gentleman before me was briefly transformed into a fanged and fuming, flashing-eyed psychopath.

It's amazing what they get up to in Chichester

I spent a few hours at the weekend in an Accident & Emergency department, getting my head patched up. Tough guy, or what?

No, I wasn't involved in a gang rumble, a football fight or a mugging; it was a more middle-class thing. Inching my way, bent double, through a friend's labyrinthine and cobwebby wine cellar, and taking a perhaps too-eager right turn towards the Romanée-Conti burgundies, I bashed my head on the sharp edge of an unseen metal junction box. Blood gushed like a garden hose. The left side of my white barnet turned a fetching shade of cyclamen, then, later, cerise. Lunch was put on hold as a kind soul drove me to Chichester Hospital, where, after I was made to watch some Grand Prix vehicles pointlessly circulating a track, a charming lady glued my cerebellum back together.

"What's it like in an A&E department on Saturday nights?" I asked. "I bet you've seen some sights. Gunshot wounds? Fatal stabbings? Axe murders? GBH with chains and machetes?" "Not exactly," she said. "This is Chichester. We get elderly people who've had a fall on Saturday evenings. And now it's summer, we get head abrasions on people who've taken up cycling. Some yachting accidents with swinging booms, of course. Oh, and people falling out of hammocks ..." And yet some still maintain that British bourgeois lives lack excitement ...