Magna Carta
http://www.bl.uk/treasures/magnacarta/index.html
Habeas Corpus Act
http://en.wikipedia.org/wiki/Habeas_Corpus_Act_1679
Bill of rights
http://en.wikipedia.org/wiki/Bill_of_Rights_1689
The unwritten British Constitution
http://www.historylearningsite.co.uk/british_constitution1.htm