The UK could face more massacres like the Cumbria shootings unless "chaotic" firearms licensing is overhauled, a police watchdog has warned.
In a highly critical report, Her Majesty's Inspectorate of Constabulary said lessons have not been learned in the wake of tragedies such as the killing of 12 people by taxi driver Derrick Bird in Cumbria in 2010.
HMIC highlighted weaknesses in arrangements for assessing an individual's medical suitability to have a firearms licence, saying they are less rigorous than the checks conducted on prospective bus drivers.
Investigators also found gun owners were illegally allowed to keep using their weapons because of application backlogs and nearly half of all 43 forces in England and Wales fail to contact referees listed by new applicants.
HM Inspector of Constabulary Stephen Otter, who led the inspection, said forces are "sometimes inexcusably compromising public safety" by failing to follow government guidance.
HMIC highlighted "fundamental gaps" in the system for checking the health of an applicant.
Currently police can obtain permission from the applicant to contact GPs to obtain details of their medical history. However, doctors are under no legal obligation to respond and police routinely write to them after the certificate has been granted.
The report called for new rules, pointing out that licences to drive a public service vehicle such as a bus require applicants to undergo medical assessments by law.
Authors highlighted the case of Harold Ambrose, a dementia sufferer who killed his wife Wendy with a licensed shotgun in May 2014, before taking his own life. Neither his GP nor local health trust informed Essex Police that his mental health was deteriorating, and they were under no obligation to do so.
Seven out 11 forces inspected experienced backlogs with renewal applications. In one example, two certificate holders were told they could carry on using their firearms legally in their force area even though their licences had expired.
The report also said:
Only four of 11 forces inspected had effective monitoring and audit arrangements in place.
Just 28 out of 43 forces in England and Wales contact referees for all new firearms certificate applications.
A total of 656 shotguns or other firearms were stolen or went missing last year.
Policing minister Mike Penning said firearms licensing is kept under review and talks have started to ensure appropriate information sharing between GPs and police.
"The UK has some of the toughest gun laws in the world and we are determined to keep it that way," he said.
Last year there were 734,000 holders of firearms certificates, covering 1.8 million shotguns and other guns.
Gun crime has been falling. Last year there were a total of 4,860 crimes recorded in England and Wales which involved firearms, excluding air weapons. This was 56% lower than the number detected in 2005/06.
Gun laws have been adapted in the wake of tragedies. Semi-automatic weapons were banned in 1988 after Michael Ryan killed 16 people.
Ownership of most handguns was later made illegal following the 1996 Dunblane shooting, when Thomas Hamilton killed 16 schoolchildren and a teacher.