Joan Smith: So what is the way to express public grief?

Yesterday morning, exactly a week after terrorists exploded four bombs in the heart of London, the capital was bathed in brilliant sunshine. At midday, buses and taxis came to a standstill while people observed two minutes' silence as a mark of respect for the victims, many of whom have not yet been positively identified. Lloyd's of London rang its Lutine bell in remembrance, as it did after the 11 September terrorist attacks on the US in 2001 and the Asian tsunami on Boxing Day.

To a generation brought up in the decades after the Second World War, used to observing a one-minute silence which held no personal meaning on Remembrance Day, it is a striking fact that this method of showing respect is being used more frequently and getting longer. In January, the silence that marked the tsunami lasted three minutes, while Spain came to a standstill for five minutes on 11 March this year, the first anniversary of the train bombings in Madrid which killed 190 people.

Critics have dubbed this phenomenon "grief inflation", and it is not an easy matter to get right: how do you weigh the anguish of the hundreds of thousands who were bereaved in the tsunami against that of a much smaller number of families who still don't know for certain whether their loved ones perished on an Underground train or a bus in Tavistock Square? For that reason alone, an officially ordained silence is an awkward means of marking such events, forcing distasteful comparisons between tragedies on different continents and on very different scales.

Then there is the contrast between natural disasters and terrorist attacks, between unavoidable calamities and those caused by human malice. After the tsunami, people raged against governments which had failed to install a warning system and delays in the distribution of aid, but no individual could be held as directly culpable as the four men who planted bombs during the London rush hour.

In addition, there was an element of moral compulsion attached to yesterday's silence, a demand that everyone mark the event in the same manner, which created a dilemma for anyone who instinctively regards silence as an inadequate response to what happened in London last week. The problem is not just that silence is passive and apolitical, but an underlying assumption that we all share exactly the same response when dozens of our fellow citizens are murdered. And that is surely where much of the commentary on London's response to the terror attacks has gone badly wrong in the past week, interpreting shock, fear, incomprehension and the simple necessity of getting to work as the spirit of the Blitz.

I am always suspicious when such national stereotypes are invoked, especially when most of us are too young to remember the war or make meaningful judgements about how those earlier generations responded. Nor can I help wondering whether what foreign observers have interpreted as traditional British stoicism in recent days isn't just the habitual resignation of commuters who are used to delays and diversions on their journeys to work.

More significantly, perhaps - and as the casualty lists have demonstrated so tragically - London in the 21st century is quite unlike the war-ravaged capital of 1945. The dead and missing include many nationalities, reflecting the ethnic and cultural diversity of a city that has not been white and homogenous for a long time. Indeed, when a Nigerian woman arrived in Britain and made an impassioned speech about her missing son, there was widespread admiration of her honesty and courage.

What we have not witnessed is a display of sentiment analogous to the extravagant public mourning that followed the death of Diana, Princess of Wales, in 1997 - a tacit acknowledgement, perhaps, of the much more profound emotional impact of the bombings. On this occasion, there is no doubt that the grief and shock are real: people have been pictured weeping near the sites of the explosions, and hugging each other in silent grief, in a way that contradicts the notion that we have all stiffened our lips and carried on with our lives.

I don't know anyone who has not discussed the bombings endlessly over the past week and if some reactions seem muted, it may be because we have also had to contend with the suspicion, horribly confirmed on Tuesday, that the bombers were home-grown. This is one of the distinguishing features from the terrorist outrages in Madrid, where public horror and outrage could be directed outwards, without the kind of soul-searching that has now gripped elements of the British Muslim community.

There is another difference which has not sufficiently been acknowledged, and it has to do with political leadership. When the Atocha railway station was bombed, the then Prime Minister, Jose Maria Aznar, summoned the Spanish people on to the streets within 36 hours, encouraging them to protest in much the same way as they had earlier denounced bombings carried out by the Basque terrorist organisation Eta. Millions responded, not just in Madrid but in big cities like Barcelona, creating stunning and intensely moving images of a country united against terrorism.

Forty-eight hours after that, Aznar's right-wing government was turfed out in a political earthquake whose shockwaves seemed to flow naturally from that popular protest; even without a general election looming, it is easy to see why Tony Blair left it to the Mayor of London, Ken Livingstone, to organise last night's vigil in Trafalgar Square. Unlike his Spanish counterpart, the Prime Minister was quick to acknowledge the likelihood that the London bombings were the work of Islamists, but I am sure he does not want us to dwell on connections between the selection of London as a target and the Iraq war.

Without the kind of leadership displayed by Aznar, Londoners were left for a whole week to respond individually to the atrocity. This is a shame, because it is normal to feel a range of emotions after such terrible attacks, and it is important to provide a forum in which they can be safely expressed. Not to do so risks the kind of lashing out we saw in the US after 11 September.

Equally, slogans such as "we are not afraid" may cheer us up momentarily, but they also make people feel ashamed when they find themselves nervously eyeing other passengers or having a panic attack on the London Underground.

There can be no doubt that the world changed, eight days ago, for Londoners and the rest of this country. Grief, fear and anger - not silence - are natural reactions. What we need now are political leaders who will neither deny nor exploit those feelings.