Britain faces new gun massacres, like the Derrick Bird shootings of 2010, unless "chaotic" firearms licensing is overhauled.
A police watchdog is warning that the public are at risk because of failures and inconsistencies in the way prospective and existing gun owners are vetted and monitored.
In a highly critical report, Her Majesty's Inspectorate of Constabulary (HMIC) say lessons have not been learned in the wake of tragedies like the killing of 12 people in Cumbria by taxi driver Derrick Bird.
They also 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.
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.
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
HMIC issued a total of 18 recommendations to police and the Home Office, adding: "What is highly likely is that, if change is not effected, there will be another tragedy."