But in the years that followed, nobody had recognised their value as historical source material.

His slick, soft-rock anthems proved equally palatable, albeit deracinated and decontextualised from all the dirt and passion of their historical source material.

Channel 4 acknowledged that the tapes were made in private but a spokesman said they were 'an important historical source'.

The internet as a historical source?

Each of the 18 cases are designed to be a discrete historical source for an area of learning.