Some cave art may have been painted over millennia

"The results so far are in line with archaeologists' hypothesis that sudden flowerings of cave art came as rapid climate change was causing Palaeolithic cultures to move quickly about Europe, first as the coldest period of the ice age approached, and then as the ice age drew to a close and inhabitable areas expanded."

"There have been surprises, though - in several caves whose art had previously been assumed to date from the same period, the new dating technique has revealed that the paintings were done in several phases, possibly over 15,000 years (25,000 years ago to just 10,000.)"

Imagine living in English caves for tens of thousands of years waiting for the ice to go away again.