By Agata Chmiel ~
This past Wednesday, the United Kingdom's Prime Minister Theresa May triggered article 50 (2) of the TFEU , or in other words, sent signed divorce papers to her European counterpart, Donald Tusk. As in formal marriage disputes, at this point it is simply too late for a blame game. While PM May's letter suggests tackling several complex matters at once, the European Union's leadership is ready for a threefold approach that is going to be reasonably spread on a timetable. First, as Tusk already laid down, Britain must regulate its financial ties (or in the EU's perspective: “debt" ) with the Union.
Once the divorce is officially over, both parties can enter into a completely new series of negotiations over their future relationship. The final aspect of this entire situation is revisiting the EU's dream of integration. Even though Brexit proved it to be far from 'everlasting' as it was originally hoped for, such current members of the EU leadership as Tusk and Juncker declare 'unity' as a “number one priority" for all Member States . What seems to be one of the underlying themes among those three aspects is the future of cooperation between the UK and the EU in the security field. Is the cooperation between British intelligence and the EU law enforcement institutions jeopardized? Will the UK's input to the cooperation on prevention of transnational organised crime diminish? Such and similar concerns are worthwhile discussing.
To begin with, PM May's letter to Tusk includes a line that has already stirred the political arena in Europe. The PM calls upon foregoing the £50bn divorce bill that the EU argues to receive and instead, focus solely on the future. Probably, such a move would not generate much dismay if it was not for this one line: “(…) a failure to reach [economic] agreement would mean our cooperation in the fight against crime and terrorism would be weakened"  as May writes to Tusk, immediately raising the question whether the UK dares to weaken European security.
One of the main recipients of such a concern is could be the European Law Enforcement Agency (Europol). So far, the relationship between Europol and the UK has been mutually beneficial. Ever since the Brexit Referendum, Europol's director Rob Wainwright has repeatedly underlined the necessity of the UK's intelligence input to support crime and terrorism prevention on the entire continent, and the value of Europol itself to the UK's national security. This March, Wainwright said openly that “Europol would be weaker without active British engagement." 
However, the UK's new government has distanced itself from information sharing and crime prevention on the same terms as it used to. Home Secretary Amber Rudd suggests a possibility of even leaving Europol, adding a seemingly dangerous claim: “We are the largest contributor to Europol, so if we left Europol then we would take our information, this is in the legislation, with us." 
Additionally, PM May told the BBC that she "think[s] security co-operation in a number of crime and justice matters is important for [Britain] (…) [but] it's not just Europol (…)".  That would mean, the EU and the UK would have to negotiate over what exactly these “crime and justice matters" will be in the future strategies on cooperation within transnational area.
Notably, these concerns relate less to security in its strictly military sense because the UK has not left NATO and, hence, is still deemed to be an active actor responsible to support other members if necessary. In fact, it is currently participating in the NATO's strategy to “deter Russian aggression" through military deployment on the Eastern flank.  Moreover, some experts suggest that Brexit might actually revitalize bilateral agreements on the military operational cooperation between the UK and individual European states. 
Overall, it seems that the concerns are nothing more than a regularly politicized trade-off between 'economy' and 'security' that, eventually, needs to balance the costs and the irreplaceable need for citizens' safety. PM May's letter formalizing Brexit's process might have stirred the political atmosphere, but perhaps this time it is worth to address it through the EU's lens. The Independent reports that Tusk and Muscat collectively regard PM May's suggestive bargaining between trade and security as a simple “misunderstanding".  Naturally, such a response does not solve the existing concerns. However, only in an atmosphere of political reason and diplomatic sensibility, both Brexit negotiations and then future talks on the EU – UK's friendship will have a chance to result in a reasonable agreement. Rand Europe follows such a recommendation, claiming that “both sides risk becoming weaker and less secure if Brexit negotiations provoke a 'zero-sum' approach to defence and security." 
It is difficult to predict the future for the next two years throughout which Brexit needs to finalize. What seems to aggravate this uncertainty are numerous Eurosceptic movements and campaigns occurring in an increasing number of Member States. As security has become the key interest of most, if not all, Europeans, the EU could have a chance to rebuild its image as an actor which uncompromisingly strives to diminish terrorism and fight (organised) crime.
 Treaty of the Functioning of the European Union (2007) “2. A Member State which decides to with- draw shall notify the European Council of its intention. In the light of the guidelines provided by the European Council, the Union shall negotiate and conclude an agreement with that State, setting out the arrangements for its withdrawal, taking account of the framework for its future relationship with the Union. That agreement shall be negotiated in accordance with Article 218 (3) of the Treaty on the Functioning of the European Union."
 Full text of the letter: https://www.theguardian.com/politics/blog/live/201...:block-58dba1bae4b0a411e9ab99cf#block-58dba1bae4b0a411e9ab99cf
 Dhingra, S. and T. Sampson (2016), “Life after Brexit: What are the UK's options outside the European Union?", Centre for Economic Performance, Brexit Analysis No. 1.; p. 5