ED Miliband has expressed his absolute determination to introduce a big and historic change to Labour's relationship with the trade unions, despite the massive financial implications it would have for his party.

The Labour leader made clear he wanted the funding change implemented before the next General Election in 2015, although it could lose the party millions of pounds.

The poll will take place five years after the Tories spent £17 million, more than double Labour's total outlay, at the last election.

Asked if he would resign if he failed to push the plans through, Mr Miliband responded: "We are going to get these changes. I am absolutely determined we are going to get these changes."

In his keynote speech in London, the Labour leader insisted he wanted to build a different kind of politics, away from the hated politics of the machine, which Falkirk represented, and towards an open, transparent and trusted politics.

He stressed how he wanted to create a modern relationship between Labour and the unions, declaring: "In the 21st century, it just doesn't make sense for anyone to be affiliated to a political party unless they have chosen to do so."

At present, three million trade unionists are automatically affiliated to Labour, paying an annual £3 fee. The plan is to allow trade unionists to choose to do so individually. Each year, the process pours £8m into Labour's coffers.

Underlining this is the defining moment of his leadership, Mr Miliband said: "We have a choice: we can take action or hide away. We are going to seize the moment Falkirk presented."

He received backing from Tony Blair, who admitted he should have made the same reforms himself when in charge of the party.

"This is a defining moment. It's bold and it's strong. It's real leadership," he declared.

Later, Deputy Prime Minister Nick Clegg made clear the Coalition was ready to work with Labour to make the principle of an opt-in to the political levy law and to allow union members to use the system to support parties other than Labour.

Most importantly, perhaps, was the response of Len McCluskey, leader of Unite, Labour's largest donor, who has for days been engaged in a public spat with Mr Miliband over Falkirk.

Having before the speech suggested the Labour leader's plan was unworkable, afterwards he was more positive, describing his speech as "bold and brave" and stressing he was comfortable about a new relationship with Labour.

But Conservative chairman Grant Shapps insisted nothing had changed. "It's still the same old Labour Party with a weak leader in the pocket of the union bosses who's unable to stand up for hardworking people."

During a question and answer session following his speech, Mr Miliband was asked about claims Johann Lamont, the Scottish Labour leader, had been sidelined over Falkirk. He replied: "Johann was obviously part of the discussion around Falkirk and it is very important she was."

Meantime, the Labour leader laid down a challenge to the other parties, announcing a Miliband government would impose a limit on MPs' earnings from second jobs. He also called for the reopening of stalled talks on the funding of political parties, repeating his offer to cap donations from individuals and businesses.

The Labour leader announced plans to establish a code of conduct for would-be election candidates and to introduce US-style primary elections for Labour's next candidate for London mayor and possibly parliamentary seats.

Falkirk MP Eric Joyce, who created the vacancy at the centre of the crisis when he quit Labour after a Commons bar brawl, said his constituency should be the first to adopt the primary method for picking a candidate, under which anyone registering as a Labour supporter would have a vote.