Andrew Grice: This could prove to be Ed's defining moment

When Ed Miliband ran for the Labour leadership on a "not Blair" ticket, he reassured his party he would not pick fights with it to win cheap headlines. In line with that, he did not seek the battle with the trade unions which erupted yesterday over Labour's support for spending cuts and a longer period of public sector pay restraint. He did not want to define himself against his party but is learning that opposition leaders need to do that to "cut through" to the public. Abolition of Clause IV, Labour's support for old-style public ownership, defined Mr Blair in voters' eyes and helped convince many that the "new" in New Labour was real. Symbols matter.

Yesterday's collision with the unions was accidental but while some Labour MPs will worry about divisions being aired in public, the row should boost Mr Miliband's standing with voters.

By highlighting Labour's support for cuts, it should help the party regain some economic credibility and answer the Conservatives' charge that it is "in denial" about the deficit.

After previous periods in the spotlight, Mr Miliband has tended to retreat to the shadows to plot his next moves. There are lots of meetings about meetings.

Yesterday could prove a defining moment in his leadership. Instinctively, he will not relish a fight with the unions and would prefer brotherly love to confrontation. But he will know that he cannot retreat now that the unions have put their tanks on his lawn. The row has given him an opportunity to be heard by the voters – and he should seize it.