How a BBC natural history crew filmed the "humpback whale heat run", the greatest animal battle on the planet.

Cameraman Roger Munns freedives below the surface to film 15m long, 40 tonne male whales chasing after an even larger female.

During the first complete sequence of this behaviour ever captured, the male humpbacks swim at high speed behind the female, violently jostling for access.

The potentially deadly battle is filmed for the BBC natural history series Life.