The British Isles are a group of islands off the north-western coast of continental Europe that consist of the islands of Great Britain, Ireland and over six thousand smaller isles.he demographics of the British Isles today are characterised by a generally high density of population in England, which accounts for almost 80% of the total population of the islands. In elsewhere on Great Britain and on Ireland, high density of population is limited to areas around, or close to, a few large cities.