No one is more worthy of being quoted on the current Brexit issue than the great English priest and poet, John Donne:
No man is an island, entire of itself; every man is a piece of the continent, a part of the main; if a clod be washed away by the sea, Europe is the less, as well as if a promontory were, as well as if a manor of thy friend’s or of thine own were; any man’s death diminishes me, because I am involved in mankind, and therefore never send to know for whom the bell tolls; it tolls for thee.
This is not from a poem, as many people assume, but from Meditation 17 in his Devotions Upon Emergent Occasions. The full text can be found at the very useful website, Luminarium, along with many other prose works and poems by Donne.
England and Wales 1636