Traditionally, royal females who have not had the luck to become queens regnant have been granted very limited roles. They have been expected to look pretty, be discreet, do charitable good deeds, and - if married to princes or kings - be quietly supportive and, above all, fertile.

Since the Second World War, as female expectations and opportunities have risen, becoming a royal woman - and remaining a royal woman - has seemed less and less an attractive proposition.

Captives' was a deliberate bridging exercise, an attempt to use detailed knowledge of what Britain was like on the inside, to reach a deeper, more variegated understanding of how its peoples experienced external adventures and aggression over a quarter of a millennium in four continents.

To be sure, political unions between European countries have often failed in the past, but usually only after relatively brief periods. Denmark and Iceland separated after 130 years; the unions between Spain and Portugal and between Sweden and Norway each lasted less than a century.