The UK's reluctance to join the Schengen Area, through concerns over loss of independent border controls, is usually cited as the reason for not joining. Britain argued that, for an island, frontier controls are a better and less intrusive way to prevent illegal immigration than other measures, such as identity cards, residence permits, and registration with the police. Consequent difficulties for Ireland, given its location and shared border with the United Kingdom (at which border points would have to be set up), would then make it very difficult for Ireland to join without the United Kingdom.