London  - British Prime Minister Gordon Brown Tuesday took on his critics in an emotional and highly personal speech aimed at re- establishing his authority after months of poor opinion poll ratings and an attempted "rebellion" against his leadership.

In what had been termed a "make or break" speech to the Labour Party's annual conference in Manchester, northern Britain, Brown acknowledged there was "concern" over the future of the party and his own presentation skills.

But in a highly personal - yet determined - speech, Brown said: "I know what I believe, I know who I am. ... I'm not going to try to be something I'm not."

He warned rebels that the public would "not forgive" the Labour Party if it continued to indulge in internal squabbling at a time of profound change and unprecedented turmoil in the world economy.

"In these uncertain times, we will be the rock of stability and fairness," said Brown, promising voters a "new settlement for a new time" and "a fair Britain for a new age."

In a reference to the slide in opinion polls, Brown said he had not come into politics to be popular, and rejected "celebrity" politics.

"I want to give the people of this country an unconditional assurance - no ifs, no buts, no small print - my unwavering focus is on taking this country through the challenging economic circumstances we face and building the fair society of the future."

Brown said the recent turbulence on the world's financial markets and the shake-up of the global economy marked a "defining moment" which required a "rebuilding of the world's financial system around clear principles."

Sound banking, transparency in all transactions and global standards of supervision were all part of a "new settlement" he would call for at the United Nations General Assembly in New York later this week.

Brown, who during his 15 months as leader has presided over an astonishing slump in his personal rating as well as that of the Labour Party, attacked the opposition Conservatives as "novices" unable to tackle the current global crisis.

Britain needed a Labour government "now more than in 1997," said Brown in a reference to Labour's landslide victory under Tony Blair, and he was confident that a united party could win another election "for the sake of our country."

The speech was hailed by trade union chiefs, who said Brown was the right man to lead Britain during a time of global economic crisis.

"We expect to see him take further steps to ease the burdens," said one.

Foreign Secretary David Miliband, seen by many as a successor to Brown in the event of a leadership challenge, said the speech had proved that Brown had "found his true voice." (dpa)