When they see the first police car arrive, the pair split up.
Blade-wielding Michael Adebolajo, 28, runs at officers head-on and his accomplice, named locally as 22-year-old Michael Oluwatobi Adebowale, advances alongside, aiming his gun at them.
The film of the 10 seconds of terror shows how Adebolajo got within two feet of the WPC who was driving the armed response BMW X5.
As he is sent sprawling to the ground by the force of the two shots, two officers jump out to cover him.
They appear not to see Adebowale aiming a handgun at them.