Thames Valley Police (TVP) have been told to improve in one of the most important aspects of policing - investigating crime.
In a report for Police Effectiveness Efficiency Legitimacy (PEEL), TVP was criticised for its handling of low-level crimes after closing some investigations too early, and for failing to record victim's contact details consistently.
It also found some officers had not received the "lowest level" of vetting clearance before joining the force, due to a historical backlog in the process.
Jason Hogg, TVP's deputy chief constable, said: “We have already taken steps to address the issues raised during the inspection.
"We are working hard to improve the quality of our investigations to ensure that we can provide justice for victims and an excellent quality of care in how we support victims through the criminal justice process.
"Her Majesty's Inspectorate of Constabulary and Fire & Rescue Services has acknowledged that they are encouraged by the action we are starting to take.
Despite the concerns, TVP was rated "good" overall for its effectiveness in reducing crime and keeping people safe, providing sustainable services to the public, and the way it treats the public and its workforce.
HM inspector of constabulary Zoe Billingham said: “I am pleased with most aspects of Thames Valley Police’s performance in keeping people safe and reducing crime.
“The force understands its communities. It tackles anti-social behaviour well and works closely with partner organisations to make sure it safeguards victims.
"Serious crime is investigated well, but the investigation of less-complex crime needs to improve.
“The force has a good understanding of demand and how it will change, including the effect of technological change. It is using this knowledge to develop financial and workforce plans for the future.
“Senior leaders continue to uphold an ethical culture and promote standards of professional behaviour well.”