In 878 the borders of Alfred the Great's Wessex were confined to a small patch of marshland in Somerset. This was Britain. Four centuries later, and the country straddled the English Channel, embracing much of what we now know as France. Six hundred years later, its boundaries were to be found in the Caribbean, the Arabian Sea, the Indian Ocean and the Sunda Strait. These, too, were Britain. Yet when - and where - did Britain begin? Is the shape of Britain led by the British - or are foreign powers more responsible for our borders than we realise? Is Britain justified in its island mentality? Will Britain ever be at ease with its own borders? And is the shape of Britain soon to change all over again?...