Britain's government declared the country was "broke and broken" ahead of an assessment of the public finances on Monday which the newly-elected Labour Party will use to blame their predecessors for a 20 billion pound ($26 billion) shortfall.

Elected to run the world's sixth-largest economy in a victory on July 4, Labour has spent much of its first three weeks in power telling the public that things are worse than expected in almost every area of public policy.

Finance minister Rachel Reeves will set out the findings of a fiscal review in a statement to parliament that will accuse the Conservative Party — which led the country for the previous 14 years — of making unfunded spending commitments to try to win public support.

"The assessment will show that Britain is broke and broken - revealing the mess that populist politics has made of the economy and public services," a statement issued by Prime Minister Keir Starmer's office said.

"It will show that the previous government made significant funding commitments for this financial year without knowing where the money would come from."

'Not shy about talking reality'

The Conservatives have dismissed Labour's widely-previewed announcement of a 'black hole' in the public finances as a fabricated pretext for tax rises it did not disclose during the election campaign.

Some economists were also sceptical, saying there were few big surprises Labour could not have foreseen before taking office.

Reeves will also reveal the date for her first budget, commission the independent forecasts that will be published alongside that budget, and set out plans for the formal spending review process that decides how much money each department gets.

She is also expected to agree to above-inflation pay awards for teachers and health workers.

It is unclear how Labour will address the shortfall it identifies. Reeves is hemmed in by-election promises not to raise rates of income tax, National Insurance social security payments, value-added tax and corporation tax.

Media reports have mooted that Reeves would use Monday's statement to pave the way for other tax rises at the subsequent budget. The Financial Times said she would delay some road and hospital building projects.

The government statement did not set out any measures, but senior Labour minister Pat McFadden said: “We will not shy away from being honest with the public about the reality of what we have inherited."