New York's mayor, Michael Bloomberg, decided it was time to act. Having wrestled with the opposing rights – Occupy Wall Street Movement's first amendment right to free speech, and the public's right to health and safety – he decided (surprise, surprise) that the latter trumped the former. An increasing number of large tents and other structures erected in Zuccotti Park made it difficult for the emergency services to ensure the protesters' public safety, the mayor claimed in a statement, shortly after the police moved in to clear the park in the dead of night and trash the tents. The mayor's purported concerns for health and safety were even less persuasive as a reason for restoring the status quo in lower Manhattan than they were when the former dean and chapter of St Paul's used the same arguments to threaten to clear protesters from the steps of their cathedral.

What follows is a new phase for the Occupy movement, not just in Manhattan and Oakland, but outside St Paul's (where protesters faced a renewed eviction attempt yesterday) and around the world. As a grassroots protest it has been astonishingly successful, not just in replicating itself in cities around the world but in starting to shift the debate away from falling markets to economic justice, from economic deficits to democratic ones. It has challenged mainstream politics and the mainstream media to respond to its agenda. And it has done so on the whole non-violently, rationally and energetically.

The universality of its appeal can be judged by its diversity, from self-identifying groups like anarchists and anti-capitalists to many who have just turned up to agree. Together they have started a debate which is surely set to outlast the physical protest itself. Whether you agree that power has been appropriated by 1%, leaving 99% disempowered, the "us" for which the Occupy movement claims to speak is clearly not to be consigned to the fringes. It is wider than congressmen or parliamentarians would have us believe.

The movement now faces the challenge of continuing what it started. It must engage in a battle of ideas, not just spaces, and needs to seek fresh ways to keep the debate going. It will survive if it does. It will fail if it becomes co-opted or marginalised. But its chances are unwittingly boosted by the likes of Mr Bloomberg. A backlash was growing yesterday, with the city comptroller John Liu saying there seemed to have been no compelling reason for the action. The mayor said every New Yorker had the right to speak out. But it seems National Public Radio, Associated Press and the New York Daily News, all of whose reporters were arrested, don't have the right to report it.