Original: A final ice age covered Britain between around 70,000 and 10,000 years ago with an extreme cold snap between 22,000 and 13,000 years ago called the Dimlington stadial (with the Last Glacial Maximum at around 20,000 years ago).
Simplified: A final ice age covered Britain between around 70,000 and 10,000 years ago with an extreme cold snap between 22,000 and 13,000 years ago which may have driven humans south out of Britain altogether.