Rank-and-file police officers are more than £6,000 a year worse off in real terms compared to 2010 when the Conservatives came to power, according to Labour analysis.
Shadow police minister Louise Haigh said it was no surprise that morale was at "rock bottom" given the pressure on officers' wages from the 1% public sector pay cap at a time of "soaring" crime.
Labour's analysis of official data and forecasts showed that officers across sergeant and constable ranks will have a projected mean annual salary of £40,512 this year, but if wages had risen in line with inflation since 2010 they would be on £46,649, leaving them on average £6,137 worse off.
It comes amid mounting speculation that Theresa May is ready to end the long-standing cap on pay rises in the public sector after a disastrous general election which saw the Tories lose their House of Commons majority.
A former top Treasury official also called on the Prime Minister and Chancellor Philip Hammond to lift the cap, saying it is unsustainable in the long-term but that they will have to cut spending or hike taxes to pay for it,
Lord Macpherson of Earl's Court, who spent a decade as permanent secretary to the Treasury until 2016, said a failure to properly cost any lifting of the 1% cap would leave the deficit unacceptably high.
Earlier this week, Defence Secretary Sir Michael Fallon said the Government fully understood that public sector workers have taken their "share of the pain" of deficit reduction and signalled that the Chancellor was looking at the issue.
The Institute for Fiscal Studies has said if public sector pay were to rise in line with inflation for the next three or four years it would cost the public purse £6 billion to £7 billion more than continuing with the cap.
Ms Haigh said: "It is no surprise that police morale is at rock bottom when the Tories have spent seven years asking them to do ever more while slashing their pay year after year.
"These stark figures show that the frontline police officers are now thousands of pounds worse off than they were in 2010, and the Government's plans to continue with the public sector pay cap will only make matters worse.
"We are now seeing disillusioned officers flooding out of the service, with resignations skyrocketing.
"Seven years of Tory cuts to police numbers and pay have left a demoralised force at its lowest strength on record being asked to fight soaring crime and record demand.
"A Labour government would end the public sector pay cap so that our police get the salary they deserve, and fund the recruitment of another ten thousand officers to restore neighbourhood policing."
The Treasury is due to send out letters within weeks setting out the remit for public sector pay review bodies for next year's pay round and Mr Hammond is under pressure to allow them greater flexibility to recommend more generous rises.
One plan reportedly under consideration could see the lowest-paid public sector workers, along with groups with the biggest retention problems such as nurses and senior civil servants, granted a pay rise at least in line with inflation next April, with restraint for others lifted in 2019.
Mr Hammond has refused to be drawn on the reports, insisting the Government must balance pay rises against increased costs.