Theresa May today vows to step up radical reforms of British policing as she warns forces they will not be "let off the hook" despite being shielded from budget cuts.
The Home Secretary will tell senior officers and local crime chiefs they will still be required to make savings even though the overall police budget is being protected.
In the latest episode of her fractious relationship with police, Mrs May is also expected to deliver a fresh rebuke against those who complain about cuts and attack wasteful spending.
Chancellor George Osborne sprung a major surprise last month when he ruled out a fresh round of reductions to the police budget. The move followed warnings about the capacity to respond to a Paris style terrorist attack.
However, in a speech to chief constables and police crime commissioners (PCCs), Mrs May will insist the settlement is "not a reprieve from reform".
She will say: " The overall policing budget is protected.
"But not the wasteful and inefficient spending that we all know still exists. Because if we are to meet the challenges that lie ahead, and if we are to ensure money is well spent, then further changes will need to be made.
"It does not let you off the hook or mean you can slow the pace of change. Nor does it insulate you from the need to look for further efficiencies.
"Quite the opposite. Now - more than ever before - there is no excuse not to deliver.
"Instead, we must redouble our efforts, force a more urgent pace, and deliver a more radical and more sustained period of police reform than we saw even in the last Parliament.
"Because with protected funding comes an even greater responsibility to spend every penny of taxpayer's money wisely, and to drive better value at every step."
Mrs May has overseen a string of reforms including the abolition of national targets and the introduction of crime maps, which the Government claims have reduced bureaucracy and improved accountability.
But she has come under repeated attack from rank-and-file leaders after officer numbers fell by almost 17,000.
The Home Secretary, who earlier this year criticised the Police Federation for "scaremongering" over the impact of cuts, will say today:"I know many of you have welcomed the Spending Review and committed to continued reform.
"I applaud that and will always do everything in my power to help you.
"But neither I, nor the public, will have any sympathy for those who complain about budget cuts - as some of you have continued to do in the past couple of weeks."
Officials said Mrs May's address will challenge chief constables and PCCs to consider how specialist capabilities, such as firearms, financial crime or cyber units, could be delivered between forces or in regional teams.
"It is not in spite of the need to find savings that we have been able to reform policing, but because of them," she will say.
"And to those who think the Spending Review gives you breathing space to relax the reforms we started five years ago, you could not be more wrong."
The decision to protect overall police spending in real terms amounts to a cash rise of £900 million by 2019/20.
Mrs May will say the decision was "important and right" and - on top of £1.9 billion of savings forces are already planning to make and £2.1 billion held in reserves - represents a "massive investment in the future of policing in this country".
However, she will warn that every force will still need to make savings year on year when their individual funding allocations are set out next week.