According to Reeves, the previous conservative government has left behind a "black hole" in the public finances of 22 billion pounds (approximately 306 billion kronor).
If we don't do anything about it, it will mean a 25 percent increase in the budget deficit this year, said the Finance Minister on Monday.
Reeves accuses the Tories of having avoided making tough decisions and putting party interests before the country's interests.
They continued to make unfunded commitments, aware that the money wasn't there, she said.
The Labour government, which took over from the conservative Tories after Labour's big election victory in July, will present its plan on October 30. It may involve cutting planned rail and road projects, reducing consulting costs, and raising taxes.
It will be a budget to fix the foundations of our economy.
The opposition dismisses Reeves' claims and argues that the new government is blaming the deficit to be able to raise taxes.
The British deficit stood at around 120 billion pounds (equivalent to over 1,650 billion kronor) during the 12 months up to the end of March, the country's latest fiscal year.
