A proposed new funding formula for police forces in England and Wales was based on flawed calculations, the Home Office has admitted.
A letter from a senior official says the way it estimated changes in the central government grant was wrong.
Police and crime commissioners said the process was a "shambles" and called for it to be abandoned.
Policing minister Mike Penning said the funding model was being "refined" in light of feedback from forces.
Forces' final allocations would not be settled until after the government's spending review later this month, he said.
Devon and Cornwall Police, one of the forces expecting to be badly hit by the proposals, said the changes could affect all 43 forces.
Thirty-one of the 43, according to its calculations, will be worse off the than the funding formula proposed last month because of the error, whereas 12 will be better off compared to that proposal - including the Metropolitan Police, whose grant will be cut by only £3 million instead of £184 million.
Lancashire's Police and Crime Commissioner, Clive Grunshaw, said: "It is incompetence on a monumental scale. It beggars belief."
Conservative Stephen Greenhalgh, London's deputy mayor for policing, said: "The main purpose of changing the police funding formula was to make the system more transparent and fairer.
"However, the current approach is shambolic and fast becoming a lottery - with a police force needing to buy the raw data to prove the Home Office sums did not add up. The Home Office must think again and postpone this review for a year."
The Home Office acknowledged errors were made but said it did not recognise the Devon and Cornwall calculations.
Police funding was cut by 18% in real terms from 2010-16, and significant further cuts are expected as the government looks to balance the economy.
Mr Penning said the old funding formula was "not fit for purpose". He added: "If we want policing in this country to be the best it can be, then we must reform further, and that includes putting police funding on a long-term, sustainable footing.
"Allocations for individual police force areas have not been set and decisions on funding will not be made until after the Spending Review reports in November."
Shadow policing minister Jack Dromey released a letter from the Home Office director general for crime and policing, Mary Calam, to the office of the Devon and Cornwall PCC in which she admitted that some of the data used to calculate the allocations was out of date and had been updated.
"I would like to again confirm that it is this updated measure that we propose to use in determining final allocations," she said.
Cumbria's Police and Crime Commissioner, Richard Rhodes, said his force could face an additional £5.8m a year cut in revenue in addition to the £9m they had been told about.
He said the error undermined the credibility of the consultation process.
"The provision of accurate percentages to allow PCCs and chief constables to assess the potential impact of proposals on individual forces is a critical part of the process," he added.
"We would therefore urge the Home Office to appoint an independent panel to review the funding formula and consultation process."