Gun owners face having their licences reviewed in the wake of the Plymouth mass shooting as police forces were also ordered to check social media accounts.

       Priti Patel, the Home Secretary, has asked all the 43 police forces in England and Wales to review their current firearm application processes and whether they need to “revisit” any of the existing 720,000 gun licences.

       New statutory rules on gun applications including compulsory checks by police with GPs on prospective owners’ mental health conditions are also to be published within weeks.

       Police checks will also be recommended on “open source” social media accounts of applicants after it emerged that police failed to trawl through the Plymouth “incel” killer Jake Davison’s online activity before last month giving him back the gun he then used to kill five people.

       Devon and Cornwall chief constable Shaun Sawyer admitted his force feared invading the 22-year-old’s privacy. Yet, in one chilling post, Davison had revealed his obsession with the 1987 massacre in Hungerford, Berks and had also liked hundreds of gun videos on YouTube.

       Police chiefs said yesterday “Ripa” rules on investigations devised before social media prevented “random” trawling of people’s internet accounts without a specific complaint.

       Mr Sawyer said: “What we don’t do, because firearms licensing is a lawful thing, is trawl the internet looking at people’s lives. That’s an invasion of privacy.”

       However, a Home Office source said: “We are bringing forward new guidance to improve how people applying for a firearms licence are assessed in future, including social media checks.

       “But today, as a matter of urgency, we are asking the police to review their practices and whether any existing licences need to be looked at again. This will help reassure people that all necessary checks have been made to keep them safe.”

       A senior policing source said a September 2020 assault allegation against Davison, which prompted police to remove his licence, should have triggered an examination of his social media and the officers investigating the case should have passed on any concerns to the firearms team.

       It is not known what medical checks were made by police on Davison who suffered mental health problems but the new rules will require police to check with an applicant’s GP and refuse a licence if the doctor fails to provide a report. The changes were recommended six years ago by HM Inspectorate of Police but have not yet been introduced.

       The Home Office source said: “Incidents such as Thursday’s horrific events in Plymouth are thankfully rare, but their impact is profound, not only on those directly affected but on the public as a whole.

       “We constantly assess what sensible and proportionate steps we can take to help prevent such terrible loss of life happening again.”