Why didn't England want to join the Schengen Area?
Schengen Area is one kind of multinational cooperation in European Union that allows free movement of people through the EU countries member. Why England doesn't want to join Schengen Area then?
My understanding is that Britain's opposition to joining the Schengen Agreement was due to its desire to maintain complete sovereignty over its borders.
Under the agreement, as you have noted, there are no border controls for people moving between countries in the Schengen Area. Britain was worried about this largely because of worries about unlimited immigration from other countries in the Area. They were also worried about the idea that other countries might let in large numbers of immigrants or asylum seekers from outside the Area. Once in, the immigrants, it was thought, would come to Brtiain.
So the overall idea here is that the British wanted to retain the ability to have more of a say over who could and could not enter their country.