Hur hur.

It’s a blessing to hear a bad-taste joke. Jokes about recent tragedies are a way of helping to make them history. Your snigger moves you safely away from the abyss and back on to firm ground.

“I don’t know any others,” he went on solemnly, begging to be challenged, then grinned. He couldn’t restrain himself.

“Except this.” And he was off.

"These bombs are just like London buses – you wait ages for one then four come along at once."

Or, more simply: "A Londoner got on a bus. Boom boom."

The taxi driver, who never went on public transport himself because when he wasn’t in his cab he had a lovely little Lambretta scooter in the garage, was pleased with himself for having entertained me. And our farewell look at each other was full of the kind of mutual approval that signals the silent relief of the British at beginning to process a trauma that is beginning to recede.

I was so relieved to hear the joke that I began to believe that – despite all those extra bombs found in the 7/7 bombers’ car, left at Luton on a week-long parking ticket – we were over the London terrorism outbreak.

But that was on Wednesday. By Thursday evening, after the second wave of bombings , I was part of the footsore army of people walking or cycling home at the end of the working day. And I was aware of the hush that had fallen over Londoners again.

The people moving through Covent Garden, and up a car-free Tottenham Court Road to Warren Street Tube, had a kind of insouciance about them. They were taking control of their destiny, getting themselves back to their TVs and families; you could see there was a quiet pleasure in taking control of the tarmac in the centre of the road, usually the preserve of buses, taxis, motorbikes and cars. They just had nothing to say.

Patiently, silently, they turned left or right when they got to the police tape and the waiting officers in their yellow fluorescent waistcoats, accepting the detour forced on them.

There wasn’t much point in asking the police officers for information. If you did, they only opened their arms wide in bewilderment and said “I don’t know”.

When I saw a posse of TV cameramen filming Warren Street Tube at about 9 pm, I opened my mouth to ask, “why are you still filming? Isn’t it all supposed to be over?” And the sound of my voice startled me in the silence. The nearest cameraman smiled, and shrugged. “I don’t know. We’ve just been told to stay here,” he answered, almost in a whisper. I melted back into the walking, whispering, quiet stream of people taking their long ways round to get back home to normality.

No one was killed in Thursday’s bombings. From the bombers’ point of view, their outing must have been a failure.

By Monday morning London was still quiet, but the fear was beginning to melt away. Streets full of walkers in trainers and office suits and cyclists in ties and office suits. Buses crowded with commuters looking anxiously at each other; top floors empty after two bomb attacks on the top floors of buses. Nervous grins and sweaty hands in the Tube as the cliche of British reserve is discarded. And the bravest opening their mouths; the first, quiet voices raised to begin the first normal conversations, between friends, behind hands. About the investigation. About the young man killed at Stockwell Tube station. But also about more normal things – work, family, holiday, where to go on Friday night.

Still, I think it will be several more days before we hear any more bombing jokes.

Slices of London: e-mail Urban Fox here