What's happening in Egypt and how serious is it?

Since Tuesday student and opposition groups have been staging protests across Egypt inspired by the uprising that toppled the former president of Tunisia, Zine al-Abidine Ben Ali, a fortnight ago. On Friday, such was the intensity of the protests that President Hosni Mubarak, in power for 30 years, sacked his cabinet and made vague promises of reform. But, as the fifth day of protests showed yesterday, the gesture did nothing to placate the crowds. Like all Arab countries, Egypt has a large youth population which has grown angry about unemployment, poverty, rising food prices and an autocratic leadership seen as corrupt and stagnated.

Who are the opposition?

Almost everyone. In an unprecedented display of unity among disparate wings of Egyptian society, middle-class students and internet-savvy young people are protesting alongside older, hardened activists and those from less privileged backgrounds. In terms of official political opposition, however, the picture is less clear. The Muslim Brotherhood, Egypt's largest - and banned - opposition group, has kept a low profile and chosen not to fully endorse the protests. Former UN nuclear chief and Nobel peace prize winner Mohamed ElBaradei is viewed by many as the strongest opposition candidate for this year's presidential elections. He returned to Egypt on Thursday and called for Mubarak to stand down - only to be placed under house arrest.

Is there a danger of an Islamist takeover?

At the moment, the Muslim Brotherhood is playing catch-up with a young, leaderless protest movement. But chaos always opens opportunities and years of oppression by the government has angered and frustrated ordinary people. The brotherhood has enormous support among the poor, encouraged by the network of charities it runs. Observers have been debating the sincerity of the brotherhood's apparent moves towards real political reform, and point to its inability to directly challenge Mubarak's government.

What are the implications for the Middle East?

Egypt is the most populous Arab nation and, as the first to sign a peace treaty with Israel, a major Middle Eastern player. A change in regime could have a big impact on the fragile peace process. But the biggest fear is of a domino effect, similar to what happened in eastern Europe in 1989, when a successful uprising encourages other "people power" movements, leaving Arab autocrats nervous and oil prices in flux.

And for the west?

As reflected in the mild comments from Barack Obama and Hillary Clinton on Friday, western politicians need to achieve the right balance between backing the people's legitimate demands and protecting their own interests. It is not good for western powers to lend their support to autocratic regimes. But it is in no one's interest to have a political vacuum in countries where extremism and violence can flourish and where much of the world's oil reserves are managed.