Tony Blair has described Labour's autumn conference as a "crucial staging post" on the way to a third general election victory.

In an article for The House Magazine, the prime minister calls for unity following deep divisions over the war in Iraq.

The Brighton conference, which formally gets underway on Sunday, is set to expose Labour splits on both the war and wider issues of public service reform.

But Blair urges his party to concentrate on "our goal of winning an historic third term".

"It is a week where our party and government must demonstrate that we retain the energy, unity and vision to continue to make life better in Britain," he says.

"We can’t rest on our achievements. We have to show again that we deserve the chance to continue in government with fresh ideas and practical policies to meet the concerns and ambitions of the country.

"I am confident that our party will rise to this challenge as we have to many challenges over the last few years."

Setting out the government's achievements in areas such as health, education and employment, the prime minister says that his programme has not "been easy".

"Continuing and accelerating this progress is not going to get any easier," he warns.

"It will need commitment and courage, energy and vision. It means renewing in power just as we did in opposition so we stay in tune with the aspirations of the hard-working majority of our country."

And, in an uncompromising message to the party's grassroots that the reform process will continue, he says that Labour must set out "a bold radical third term agenda".

Despite Blair's call for unity, however, splits are certain to emerge at the conference.

The Iraq war has deeply angered many activists, while plans to introduce greater choice in health and education have also prompted concern among some MPs and party members.

The chancellor's pledge to axe thousands of Whitehall jobs has also gone down badly with key unions.

Gordon Brown's previous conference appearances have generally been welcomed by those on the left of the party, but this year observers will be closely analysing the reception he receives.