After taking on Rupert Murdoch, Ed Miliband has stood up to the most feared editor on Fleet Street - Paul Dacre. In a lengthy piece in tomorrow's Daily Mail, he takes aim at the paper for running a gutter attack on his father, Ralph, under the headline "The man who hated Britain". He writes:

It’s part of our job description as politicians to be criticised and attacked by newspapers, including the Daily Mail. It comes with the territory. The British people have great wisdom to sort the fair from the unfair. And I have other ways of answering back. But my Dad is a different matter. He died in 1994. I loved him and he loved Britain. And there is no credible argument in the article or evidence from his life which can remotely justify the lurid headline and its accompanying claim that it would "disturb everyone who loves this country".

Many politicians have seen members of their family traduced by the Mail but none have ever responded as Miliband has. When they and their relatives were attacked, Tony Blair and Gordon Brown didn't confront Dacre, they appeased him. Miliband has taken a different path; this will rightly come to be seen as a defining moment of his leadership.

After the Mail alleged that his father loathed Britain on the basis of an adolescent diary entry, his son points to his record of service in the Royal Navy, mentioned only in passing by the paper: "He arrived, separated from his mother and sister, knowing no English but found a single room to share with my grandfather. He was determined to better himself and survive. He worked as a removal man, passed exams at Acton Technical College and was accepted to University. Then he joined the Royal Navy.

"He did so because he was determined to be part of the fight against the Nazis and to help his family hidden in Belgium. He was fighting for Britain.

"When I was growing up, he didn’t talk much about the Holocaust years because it was a deep trauma for both sides of my family. But he did talk about his naval service.

"The Daily Mail’s article on Saturday used just a few words to brush over the years my father spent fighting for his adopted country in the Second World War. But it played a bigger part in his life than that."

But while defending his father against the Mail's specific charges, he also uses the piece to make a wider argument about press standards and ethics. Here's the closing passage:

Britain has always benefitted from a free press. Those freedoms should be treasured. They are vital for our democracy. Journalists need to hold politicians like me to account - none of us should be given an easy ride - and I look forward to a robust 19 months between now and the General Election. But what appeared in the Daily Mail on Saturday was of a different order all together. I know they say ‘you can’t libel the dead’ but you can smear them. Fierce debate about politics does not justify character assassination of my father, questioning the patriotism of a man who risked his life for our country in the Second World War, or publishing a picture of his gravestone with a tasteless pun about him being a ‘grave socialist’. The Daily Mail sometimes claims it stands for the best of British values of decency. But something has really gone wrong when it attacks the family of a politician - any politician - in this way. It would be true of an attack on the father of David Cameron, Nick Clegg, or mine. There was a time when politicians stayed silent if this kind of thing happened, in the hope that it wouldn’t happen again. And fear that if they spoke out, it would make things worse. I will not do that. The stakes are too high for our country for politics to be conducted in this way. We owe it to Britain to have a debate which reflects the values of how we want the country run.

With this intervention, Miliband has drawn a line in the sand, signalling that, unlike previous leaders, he will not tolerate press abuses for fear of political retribution.

In the striking section on "leadership and character" in his conference speech last week, he declared: "The real test of leadership is not whether you stand up to the weak, that’s easy; it’s whether you stand up to the strong and know who to fight for." Today, Miliband has shown that he is prepared to live up to those words.

Whether or not they share his politics (and the comments section of the Mail's website suggests many readers take a more favourable view of Miliband's proposed energy price freeze than their paper), Mail readers will respect the simple decency of a son coming to the defence of his father. Milband's article is another important step towards showing the country what kind of leader he is.

Update: While publishing Miliband's response, the Mail has also unbelievably reprinted the orginal piece and an editorial defending its actions. A Labour spokesman told me: "Ed Miliband wrote his right to reply article because he wanted to state clearly that his father loved Britain. He wanted the Daily Mail to treat his late father's reputation fairly. Rather than acknowledge it has smeared his father, tonight the newspaper has repeated its original claim. This simply diminishes the Daily Mail further.

"It will be for people to judge whether this newspaper's treatment of a World War Two veteran, Jewish refugee from the Nazis and distinguished academic reflects the values and decency we should all expect in our political debate."