Leading article: A message from the many stifled by the violence of a few

There was comfort and distress to be drawn in almost equal measure by all parties to the protests staged in central London at the weekend. The trade unions, which organised the March for the Alternative, would have been gratified at the turn-out and the orderliness of the main protest. They had hoped in advance for at least 100,000 marchers; anything below that would have disappointed. On the day, the number was at least twice, if not three or four times that. The march was good-natured and well marshalled – by the unions themselves – and participation went beyond aggrieved public-sector employees.

That was the upside for the unions, and for the Labour Opposition. It also helped to vindicate Ed Miliband's decision to address the rally in Hyde Park – an appearance that some feared would reinforce the idea that he was in the pocket of the trade unions – and gave him a neat attack-line against the Government. "This is the Big Society," he said, gesturing to the crowd before him, "the Big Society united against what your Government is doing to our country." There were enough protesters to make that assertion just plausible.

Very soon, however, the balance of advantage started to look quite different. A contingent of protesters from UK Uncut had marched with the main procession. Before reaching Hyde Park, however, at least some of them filtered away to attack familiar targets on Oxford Street, such as Topshop and bank branches. So long as their activities were restricted to Oxford Street, it was just about possible for the two protests to remain separate in the public mind. By the time the breakaway groups swooped south to Piccadilly, where they mingled with those departing from Hyde Park, everything had become much more confused. And by late evening, when police and protesters clashed in Trafalgar Square, the scenes of violence and destruction had thoroughly trumped the happier scenes of families on the march.

This is where the consolation for the Coalition came in. The large numbers made it hard for ministers to pass over the march as a self-interested event of no wider political significance, even if they did try to cast it as predominantly reflecting the concerns of the public sector. Pictures of injured police and masked youths smashing windows and cash-points, however, came to their aid and could not but taint the day of protest as a whole. It is no wonder that trade-union leaders moved quickly yesterday to insist that the actions of a few hundred people should not be allowed to detract from the main message of the official protest. But this is, to an extent, what happened; the force of the pictures made that inevitable.

There were pluses and minuses, too, for the police. The relatively light controls on the official march seemed to work well. Despite fielding around 4,500 officers, however, the police still seemed to be caught off-guard when such predictable targets as Topshop were targets, and such symbols of wealth and privilege as the Ritz and Fortnum & Mason. Of course, Saturday presented no simple task: here was a single protest, with an overwhelmingly peaceful majority and a minority hell-bent on trouble. But the police seemed, despite their much-publicised use of Twitter and the like, still to be vastly less nimble than the protesters and – as was apparent from earlier student protests – to have no register between light and excessive.

The Opposition, trade unions, and the thousands of marchers will all take some comfort from Saturday's march, though it left the "alternative" they were marching for as hazy as it had always been. The effect of the violence, though, is to leave the political stakes little changed – and, regrettably, a bad taste that is likely to linger.