Winterwatch: Blakeney Point seals filmed at night

The "secret" and "highly charged" nocturnal life of England's largest seal colony, based on the north Norfolk coast, has been filmed for the first time by BBC Winterwatch.

A military-grade thermal imaging camera has revealed young bulls "sneaking" into territories under cover of darkness in the hope of mating with mature bulls' harems without being noticed - often resulting in fighting on the beach.

Winterwatch presenter Iolo Williams said the footage from the Blakeney Point reserve was "incredible".

"Sitting on the reserve under moonlight with more than 4,000 seals was the experience of a lifetime," he said.

Winterwatch returns to BBC Two at 21:00 GMT on Monday 19 January.