British finance minister Rachel Reeves on Monday will vow to "rebuild Britain" after 14 years of Conservative leadership, warning of "difficult decisions" in a speech at the Labour Party conference.

The speech, which comes a little over a month before the ruling Labour Party's first detailed budget, will be closely watched by investors amid fears of tax hikes.

The government of Keir Starmer, who became premier after a landslide victory by his centre-left Labour party in a general election in July, has blamed the defeated Conservatives' administration for a £22-billion ($28 billion) "black hole" in public finances.

UK state debt in August reached a landmark high of 100 percent of the country's gross domestic product -- its total annual output -- a level unmatched since the early 1960s.

Starmer previously warned Britons that the budget announcement on October 30 would be "painful", with tax rises and spending cuts expected.

Reeves in her speech Monday is expected to vow a "budget that will rebuild Britain and deliver the change Labour promised", and to establish economic growth as the government's "number one mission".

She will say she believes in delivering a "better Britain, a Britain of opportunity, fairness, and enterprise".

"I know that promise has felt far off in recent years. As our growth, productivity and family incomes have fallen behind," she will add, announcing a "decade of national renewal".

"We will make the choices necessary to secure our public finances and fix the foundations for lasting growth," the minister will say.

While "difficult decisions" will be made, she will warn, "there will be no return to austerity" and taxes will not be raised on working people.

Labour has already pledged to axe a winter fuel allowance for 10 million pensioners -- a vehemently criticised decision.

Sharon Graham, general-secretary of the trade union Unite, slammed what she called Starmer's "cruel policy".

"The priority that I'd like to hear from him is that he's going to reverse the decision" to scrap the boost payment, Graham told Sky News.