The Schengen agreement allows countries to remove their internal borders and allow people to travel without checks from country to country.

Schengen countries

Austria Belgium Denmark Finland France Germany Greece Iceland Italy Luxembourg The Netherlands Norway Portugal Spain Sweden

The agreement emerged outside the framework of the European Union, and was initially signed by Belgium, France, Germany, Luxembourg and the Netherlands in 1985.

Ten other countries - not all EU member states - have since joined them.

As freedom of movement is one of the main objectives of the European Union, the Treaty of Amsterdam agreed to incorporate Schengen into EU law.

But the UK and Ireland remained outside the agreement due to fears of terrorism.

Iceland and Norway signed an agreement with the EU in 1999 to involve them with the development of Schengen.

The agreement came into force in 1995 but has been troubled by fears about illegal immigration and drugs trafficking, particularly from countries such as Italy and Spain which have vulnerable coastlines.