Martha Kearney discovers the Ice Age ponds in Norfolk, called pingos, which are being brought back to life, and provide a home for the Northern Pool Frog. It's the UK's rarest amphibian and had become extinct in this country, but it's now breeding there again and Martha is keen to see one. With 400 pingos, Thompson Common is the most important site for pond wildlife in the country and also holds a precious store of seeds
