Mahmoud, my driver in Cairo when I reported from Egypt last year, didn't talk much about politics, and – an understandable precaution – kept his views to himself unless he was asked a direct question. But when he dropped me off at the airport, he launched into a sharp attack on the Mubarak regime. 'The Egyptians are a very patient people by nature, but their patience is running out,' he said. 'They could explode.' (Once his calm returned, he begged me not to mention his name, which isn’t in fact Mahmoud.)

I thought Mahmoud's warning was the sort of crystal-ball punditry you hear from taxi drivers throughout the developing world, where life continues to grind on as usual even though autocratic governance, corruption and poverty give people every reason to revolt. Leftist militants, reformist politicians, Muslim Brothers and human rights activists had been telling me for the previous two weeks that, for the moment, the regime had been reasonably successful in neutralising dissent, that Egyptians were too caught up in everyday worries to mobilise politically, and that the hopes raised by the Kifaya protests of 2005 had collapsed.

But that was before the murder of Khaled Said, a 28-year-old Alexandrian beaten to death last June by plainclothes officers for asking whether they had a warrant when they searched him. That was before the flagrant rigging of the parliamentary elections in December, which left the Muslim Brotherhood – the country's largest opposition movement – without a single seat. That was before the New Year's Day bombing of a Coptic church in Alexandria, in which 23 died, followed by the usual official claims that there are no sectarian tensions in Egypt. And that was before the popular uprising against the regime of Zine Ben-Ali in Tunisia.

Yesterday, tens of thousands of demonstrators – men and women, young and old, working and middle-class, religious and secular – took to the streets in a 'Day of Rage' protest against Mubarak, who has ruled the country since 1981. The protests weren’t restricted to Cairo: there were demonstrations in Alexandria, Suez and the Nile Delta village of Mahalla, a centre of labour insurgency in recent years. Inspired by the Tunisian uprising, the protesters showed extraordinary defiance and courage, going so far as to tear up a poster of Mubarak in Tahrir Square in central Cairo: something unimaginable until yesterday. Outside the offices of the ruling National Democratic Party, a crowd of a thousand chanted: 'Mubarak, your plane is waiting for you' (Zine Ben-Ali fled by plane from Tunis to Saudi Arabia). Protests in Egypt usually involve a few hundred (or a few dozen) people, vastly outnumbered by police; this time, the relation of forces was reversed.

Caught off guard, the police responded with tear gas, water cannon, rubber bullets and live ammunition; three protesters in Suez were killed, more than 800 have been arrested, and the regime has moved to ban demonstrations in the capital. Predictably, Mubarak's spokesmen in government and the press have blamed the protests on the Muslim Brotherhood, but no one takes these claims seriously: the Brothers did not even participate officially. The chief organisers were internet activists involved in the campaign to remember Khaled Said. He has become Egypt's Mohamed Bouazizi, though it wasn't until Bouazizi's self-immolation – and the Tunisian revolution – that Egyptians mobilised en masse in Said’s name. (The Egyptian government is now blocking Facebook, where a page called ‘We Are All Khaled Said’ has been used to organise the protests.)

Despite the Mubarak regime's efforts to invoke the spectre of the Muslim Brotherhood, Egyptians aren't demonstrating for an Islamic government any more than the Tunisians were; they're demonstrating for an honest government – one that will improve education and infrastructure, reduce poverty and inflation, end the Emergency Law, stop torturing people in police stations, stop doing the bidding of the US and Israel in Palestine, stop rigging elections, and, above all, stop lying to them. And whatever their differences, they are united in the conviction that neither Mubarak nor his son Gamal, who is being groomed to succeed him, is capable of meeting these demands. As one young activist said to me last year, 'We need a radical shake-up. We have a saying in Egypt that you can't make a sweet drink out of a rotten fish.'

Is this the explosion Mahmoud was talking about? That remains to be seen: a day of rage does not make a revolution. But it's the most dramatic expression of popular anger since the 1977 Bread Riots, which were crushed by force at the cost of 800 lives, and it could be a rehearsal for what’s to come. Revolution in Egypt would have enormous consequences for the region, as the US – Mubarak's indispensable source of protection – well knows. Egypt is America's closest Arab ally, a key partner in the 'peace process' and in the policing of the Gaza Strip: it is as central as Tunisia is peripheral. And so, as police were dispersing protesters in Tahrir Square, Hillary Clinton did her best to scatter seasoning on the rotten fish: ‘The Egyptian government is stable and is looking for ways to respond to the legitimate needs and interests of the Egyptian people.’ Later that day in his State of the Union address, Barack Obama hailed the people of Tunisia, but said nothing about the Egyptians who hoped to repeat their example, and in whose capital city he had delivered a grand speech full of promises yet to be fulfilled.