In itself, refusing to accede to an international cooperation agreement is not confusing. After all, states have different interests and therefore pursue different political agendas. For realists, mystery would not happen at all. Under conditions of lawlessness, States would cooperate only in the event of a threat. Liberal and neorealist approaches in the theory of international relations accept cooperation as a means of making profits for all actors involved. In turn, constructivists would argue that states are part of a structured relationship that results from the interrelationship between states and, increasingly, other actors in world politics. Cooperation within this structure is not unlikely, but it is to be expected. This is even more likely if institutional arrangements have been deliberately established to strengthen cooperation between states such as NATO, WTO, NAFTA, UN, EU and Schengen. The disagreements relate to the use of the term “according to” in the contract. British government lawyers have repeatedly asserted a different interpretation of the term, giving a broader definition. They claim that this is any legislation with moc content.
On the other hand, Denmark has a more rigid derogation from the area of freedom, security and justice. While the 1992 Edinburgh Agreement stated that “Denmark will participate fully in cooperation in the fields of justice and home affairs”, the 1997 Treaty of Amsterdam contained a protocol exempting Denmark, under EU law, from participating in these policies, which are instead implemented on an intergovernmental basis with Denmark. The exception is the Schengen Visa Regulation. If a measure building on the Schengen acquis is adopted, Denmark will have six months to decide on its implementation. If Denmark decides to implement the measure, it will remove the power of an international agreement between Denmark and the Schengen states. If Denmark does not implement a Schengen measure, this could lead to its exclusion from the Schengen area.  At the same time, intergovernmental agreements have been concluded between the EU and Denmark to extend EU regulations adopted in the area of freedom, security and justice to countries in which Denmark cannot participate directly due to its opt-out. These include the Brussels Convention and the Dublin Convention. The UK is also not part of the borderless Schengen area.
The agreement, which allows travel across the EU without the need for visas or passports, does not extend across the English Channel (or the Irish Sea). Neither the United Kingdom nor Ireland are part of the Schengen area. The United Kingdom and Ireland participated in certain aspects of the Schengen Agreement, such as the Schengen Information System (SIS), from 2000 and 2002 respectively. The Schengen Agreement abolished border controls between Member States. When the 1997 Treaty of Amsterdam included it in the EU Treaties, Ireland and the United Kingdom (then a Member State) received derogations from the implementation of the Schengen acquis, as they were the only EU Member States not to have signed the agreement. However, the Protocol on the Schengen acquis provides that they may, on a case-by-case basis, apply to participate in the Schengen measures if they so wish, subject to the unanimous consent of the other participating States. Ireland only joined the UK to adopt this opt-out option in order to keep its border with Northern Ireland open via the Common Travel Area (CTA).    Before the renewal of the CTA in 2011, when the UK government proposed to require passports for Irish citizens to enter the UK, calls were made for Ireland to join the Schengen area.  In response to a question on the subject, Bertie Ahern, the Taoiseach in office at the time, said: “When asked if this was the end of the common travel area and if we should join Schengen, the answer is `no.`”   The opt-out has been criticised in the UK for hampering the country`s ability to fight cross-border crime due to its inability to access the Schengen Information System.  The Schengen Agreement abolished border controls between Member States.
The UK and Ireland received derogations from the implementation of the Schengen acquis when the 1997 Treaty of Amsterdam included it in the EU Treaties, as they were the only EU Member States not to have signed the agreement. However, the Protocol on the Schengen acquis provides that they may, on a case-by-case basis, apply to participate in the Schengen measures if they so wish, subject to the unanimous consent of the other participating States. The opt-out has been criticised in the UK for hampering the UK`s ability to tackle cross-border crime due to its inability to access the Schengen Information System.  Although the UK is not part of the passport-free Schengen area, it has nevertheless used the Schengen Information System, a government database used by European countries to store and disseminate information on people and goods. This has allowed the UK to share information with countries that are part of the Schengen Agreement, often to negotiate law enforcement.  It takes its name from the city of Schengen in Luxembourg, where the agreement was signed in 1985. It entered into force in 1995. All Member States, with the exception of Denmark, have adopted the euro or are required to do so by law. The Maastricht Treaty of 1992 contained protocols on the United Kingdom (then a Member State) and Denmark, which gave them derogations from the right to decide if and when they would join the euro. Denmark then notified the Council of the European Communities of its decision to withdraw from the euro, which was included in the 1992 Edinburgh Agreement, a Council decision taken in a Danish referendum in 1992 following the first rejection of the Maastricht Treaty.
The aim of the agreement was to support its adoption in a second referendum, which it did. The Danish decision to withdraw was then formalised in an amended protocol under the Lisbon Treaty. The 1992 Edinburgh Agreement guaranteed Denmark that it would not be obliged to join the Western European Union, which was responsible for defence. In addition, the agreement provided that Denmark would not participate in the discussions or be bound by EU decisions with defence implications. The 1997 Treaty of Amsterdam contained a protocol formalising this derogation from the EU`s Common Security and Defence Policy (CSDP). As a result, Denmark is excluded from foreign policy discussions with defence policy implications and does not participate in foreign missions with a defence component.  The attacks of 13. November in Paris, during which 130 people were killed, led to an urgent overhaul of the Schengen Agreement. The ETIAS travel authorisation gives access to all the countries covered by the Schengen Agreement, i.e. the ETIAS and Schengen countries are the same, an ETIAS authorisation is effectively a Schengen visa. Under Protocol 19 to the Treaty of Lisbon, the UK has three months to respond to any EU proposal submitted under the Schengen Agreement.
If it does not alert the Council, if it wants to unsubscribe, it is automatically bound by the new judgment. From an empirical point of view, the document is based on the hearings on Schengen that took place in the Committee of the European Communities of the British House of Lords.  It is argued that the speech presented in the minutes of these hearings puts forward an interesting perspective on British border policy that facilitates a look at the Schengen Agreement and its impact on governance between Europe and the nation-state. The hearings suggest that britain`s “no” to Schengen may not be sufficiently explained in reference to British Euroscepticism. A more detailed examination of other possible factors relevant to decisions on supranational rules in key policy areas is therefore needed. For example, the dual nature of standards (stable and unstable) as well as the level of construction of standards (national and supranational) are decisive factors in the Schengen equation not only for the United Kingdom, but for all participating Member States. .