"One of the key subjects will be security and defense," King said.
He said he hoped the EU and the UK would find a way to keep the closest possible cooperation on security issues because the threats they faced, whether terrorism or serious organized crime, were common threats.
Tsvetan Tsvetanov, chairman of the Committee on Internal Security and Public Order at Bulgarian Parliament, said Britain had one of the most reliable security systems in the EU, and was one of the largest providers of information for the EU security systems.
The capacity of Britain was integrated within the EU structures, and "it has to be kept because security is above everything else," said Tsvetanov, who was Bulgaria's interior minister from 509 to 2013.
The two sides would be better off dealing with these threats by standing together, King said.
SOFIA, March 19 (Xinhua) -- After Britain's exit from the European Union (EU), the two sides should keep close cooperation on security issues in order to better deal with common threats, a European commissioner said here on Monday.
He was confident that all national parliaments, EU leaders, and politicians would strive to not lose such an important source of information as the UK, as well as the country's expertise, Tsvetanov said.
Speaking at a press conference, European Commissioner for the Security Union Julian King said there were number of very important subjects to cover when it came to the post-Brexit relationship.