Strathclyde Police are struggling to reply to calls from the public between late afternoon and the early hours of the morning, a report has found.
The report called for a review of shift patterns
The HM Inspectorate of Constabulary study found the force was "efficient and effective", but needed to review shift and crime recording systems.
It delivered a "good" service to the people of the Strathclyde force region.
But chief inspector of constabulary Andrew Brown said Strathclyde Police's new shift system had been unsuccessful.
"Core operational groups are struggling to meet requests for assistance from the public, particularly from late afternoon through to the early hours of the morning," said Mr Brown.
He recommended that the force should amend or replace the system, taking into account requirements for officers to attend court following a night shift.
The report was addressing a potential skills shortage arising from the large number of officers recruited during the 1970s who are due to retire next year.
The force had invested "significant resources" in training, accounting for £9.3m or 2.1% of its annual 2003/04 budget.
Mr Brown said: "Shift systems are important for the public to ensure optimum availability of resources to provide a policing service, but they also have significant personal consequences for the police officers and support staff who have to operate them."
The primary inspection - which is carried out every five years with two 18-month review inspections in between - also found the force's crime recording system was "limited".
The move to a centralised information system in October last year, coupled with the adoption of the Scottish Crime Recording Standard, did not go smoothly.
Strathclyde provides policing for about 2.2 million people
Mr Brown said the move gave rise to a backlog of some 5,900 records still to be entered into the crime system by the end of the financial year to March 2004, which had impacted on other crime management processes.
The force was "confident" in its recovery plan to clear the backlog, he said.
But the report also praised the force's "challenging" programme for change and revised business planning systems.
'Work in progress'
Mr Brown said: "This force is responding well to that challenge and has earned a high reputation for strong and effective partnership working, the investigation and management of serious crime and the planning and policing of major events.
"At the time of the inspection there was much work in progress and HMIC will review these areas fully during the review inspection in 18 months' time."
Mr Brown, lay inspector Jane Irvine and assistant inspector Kenny McInnes undertook the inspection during April and May of this year.
Strathclyde Police is responsible for policing 12 local authority areas, covers a geographical spread of more than 5,300 square miles and a population of about 2.2 million.
With an annual budget of some £450m, the force employs about 7,300 police officers and 2,200 support staff.