Just one in 40 police officers are available to respond to 999 calls in some areas, it has been revealed.
Startling figures in a watchdog's review showed only 2.5% of officers on duty in one area were allocated to "response duties".
The report by Her Majesty's Inspectorate of Constabulary said there were 800 officers on an afternoon shift in a command area of one unnamed force, but only 20 free for emergency response.
In another force, 50 were booked on duty but only three - 6% of the total - were allocated to "incident management".
It also disclosed that police dispatchers routinely downgrade emergency calls to relieve pressure on the system.
Controllers told inspectors that patrol officers sometimes questioned why they were being sent to particular calls, and even failed to respond.
"In some cases where patrols do not respond or make themselves unavailable, dispatch or control staff admit that they downgrade incidents in order to alleviate pressure on themselves," the document said.
"In other cases, they upgrade non-emergency incidents in the knowledge that only immediate and priority calls will have any chance of being resourced."
A review of the way calls were prioritised by Merseyside Police last October found 1% of a sample had been incorrectly graded - amounting to 500 calls a month.
Some patrol officers fail to make good use of their time on duty unless closely supervised by their sergeant, the report found.
