Great Britain was explored in prehistoric times. No records remain of who did it or of precisely when.

Norman Ault has written:

'Life in ancient Britain' -- subject(s): Antiquities, Man, Prehistoric, Prehistoric Man

Historians commonly refer to England in this time period as Prehistoric Britain, as there was no designated name for the area in that time. Sub-periods of the time were named according to common prehistoric ages, but instead have the "Britain" namesake in them (Stone Age Britain, Bronze Age Britain, etc.), eventually reaching the period known as Roman Britain.

Barry M. Marsden has written:

'Prehistoric Britain'

Yes, mines have existed in Britain since prehistoric times and they were many mines in Victorian Britain furnishing the coal and metal ores that British industry needed.