THE MURDER of Tom ap Rhys Pryce has really got under the skin of London’s professional class. When a 31-year-old Cambridge-educated lawyer is viciously stabbed to death in a Tube station for no apparent reason, it plays to our deepest fears of what happens when parallel worlds collide.

“I live on the Bakerloo Line too,” I’ve heard many say this week. “He was me — all of us.” The optimistic young man on his way up, living with his fiancée on the fringe in Kensal Green — not wealthy Kensington — carrying his downloaded wedding plans. The archetypal City worker whose death was apparently treated so lightly that a black man in a white pork-pie hat nonchalantly produced his Oyster card the following morning, then just ambled away when the ticket machine rejected it. A shocking, grubby finale to an unspeakable event.

We cannot shake it. The grainy CCTV shots of Mr ap Rhys Pryce’s last unsuspecting moments ride on top of an accumulation of other recent images in our minds. The banker John Monckton and his wife, struggling in vain to close their front door against a junkie on bail and a murderous thug on early release. The security chain swinging loose, his shouts of “No, no no!” and all the futile gestures that intelligence makes when confronted with dumb brutality. Richard Whelan, 28, stabbed six times on the upper deck of the No 43 bus for standing up and politely asking a black youth to stop throwing chips at his girlfriend. The street lights passing on the Holloway Road, the fatal lunge, the dizzy shock of collapse.

These images run like a constant commentary in my head. I, born and bred in London and used to blithely wandering the streets, now see would-be attackers out of the corner of my eye. I grasp the keys in my pocket in a pathetic, premature gesture of defence and defiance. Statistically, I know that these horrific events are still highly unusual. But they are amplified because they feel so close. They loom large in monochrome: black on white killings, fitfully sketched on CCTV. An Irish-born businessman told me this weekend that he felt London was turning into Johannesburg. An overstatement, surely, but heartfelt.

We abhor randomness. We search for motive where there is none. We seek to engage rationality, but find only hate. In a city driven by ambition, this violence does not fit the lexicon. It is senseless, gratuitous, the desire to strike even when all the cash is handed over. The realisation that this brutality is not negotiable — that there was nothing the victims could have said or offered to stay alive — brings on a queasy vertigo. I feel a heightened consciousness of the fragility of intelligent life, a sudden tenderness towards bicycling professors, nerdy executives, even the witnesses behind the windows in Mr ap Rhys Pryce’s street.

What are we supposed to conclude? That we must stand stock still in the face of violence, as the Asian man did who was robbed by the same gang 30 minutes before Mr ap Rhys Pryce was killed? It is possible, although we do not know, that the lawyer did try to fight back in some way. Some of my neighbours recently hired a private security firm after a spate of muggings. But is that really the answer in the long term, to seal off the community? Should we all run from the station to one’s front door, gripping our keys and holding out our wallets to strangers?

My powerful mental pictures are somehow erasing the daily courtesies: the hand-up with the pram, the black teenager in the hoody who gives me his seat on the Tube and winks a smiling “so there”. The fact is that “stranger murder” is still relatively rare in London, and those at most risk are poor and black. The number of murders has fallen. Since April last year there have been 130, excluding the July bombings. That compares with 144 over the same period the year before.

The great wheel of capitalism turns, raising some up to heights they never dreamt possible. That is the great achievement of this city. But those on the wheel rarely see those who languish off it. It is only when they venture out of Clapton’s murder mile or Loughborough Junction that they come into focus. Meanwhile, the middle-class advertising and music set, who slope to work in beanies and trainers to “fit in”, as scared as anyone of attracting hostile attention, are busy blasting minds with a different, even more powerful set of images.

Forget the TV watershed: go to the gym any morning and see how MTV gyrates to a synthesis of glamour and brutality first perfected by Stanley Kubrick. Watch the software industry deny yet again the obvious conclusion found by a recent American study, that violent computer games make people more aggressive. Read the fawning reviews of gangsta rap by middle-class white boys who have no idea what it is like to live in the world it describes.

Tomorrow the film Get Rich or Die Tryin’ opens in Britain. Its hero is the rapper Curtis “50 Cent” Jackson, whose album of the same name contains the usual litany of guns, gangs, bitches and blood. The BBC’s Urban Review says of the album that Get Rich or Die Tryin’ is “the antithesis to the pop-looped chart-friendly sound of mainstream hip hop”. How cool, how clever, how naive.

Reviewers always mention, with a sort of reflected pride, that “50 Cent” has been shot nine times. Their fascination was not dented one iota by the adverts showing him carrying a baby in one hand and a gun in the other. The Advertising Standards Authority ruled that the advert “gave the impression that success could be achieved through violence”. Universal Music Group defended the imagery, stating it was meant to “portray 50 Cent’s struggle to escape the hardened streets of Queens, New York”.

Come off it. We must keep the danger in perspective, but we must also stop glorifying a world that is colliding with ours.

camilla.cavendish@thetimes.co.uk

Times Recommends

• Five golden rules for regulating banks
• Uighurs’ cry echoes round the world
• It is not just democracy that is illegal