A crucial aspect of Theresa May's Brexit strategy poses a "direct threat to national security" Nick Clegg has said.

Leaving the jurisdiction of the European Court of Justice, which is a fundamental tenet of the Prime Minister's Brexit plans, is likely to mean the UK would lose access to the EU's database on the whereabouts of criminals and terrorists, which British law enforcement agencies currently look at thousands of times a day.

The second generation of Schengen Information System database, known as SIS II is a database of "real time" alerts about individuals of interest to national police forces throughout EU member states. Information on thousands of people wanted under the European Arrest Warrant is maintained within it, including those suspected of fighting jihad in the Middle East and elsewhere.

UK police and security services queried the database over half a billion times in 2016 - equivalent to 16 checks a second.

Mr Clegg claims that access to the system is open only to countries who under the legal jurisdiction of the ECJ. It is by no means certain that the UK would lose access to it in the highly likely event that it leaves ECJ jurisdiction, but no other country has ever done so.

Mr Clegg said: "Theresa May's extreme approach to Brexit will have the direct consequence of severing our ties to a fantastically useful weapon in our armoury against terrorism.

"By refusing to accept a role for the European Court of Justice in policing this European-wide database, she has ruled out our future participation it.

"It is hard to overstate the importance of this database. We check it 16 times a second, looking for security threats that have been flagged to us by other European countries. And we use it to tell other countries to stop and question people who we think are potential terrorists.

"This is Euroscepticism gone mad. If she fails to back down, Theresa May's approach to Brexit poses a direct threat to our national security."

The Government's own Brexit white paper published earlier this year specifically mentions the importance of SIS II information, noting that from April 2015 to April 2016 "over 6,400 foreign alerts received hits in the UK, allowing UK enforcement agencies to take appropriate action, whilst over 6,600 UK-issued alerts received hits across Europe".