The seven remaining contenders spend 48 hours undergoing the most psychologically gruelling stage of the training, designed to test their ability to resist interrogation. The recruits are hooded and exposed to endless white noise, and face brutal tactical questioning from a specialist team, while those who endure this experience face an even greater challenge on the highest point on the island.

The recruits go on the run across the rugged landscapes of the Inner Hebrides in a challenge designed to test their ability to evade and escape from a pursuing enemy. With limited rations and little sleep, the recruits find themselves ground down in a process where only the strongest will be able to keep going.

The recruits work in pairs as they tackle the threat of chemical warfare and execute a fast-paced extraction in near-freezing water. Then it's time for brutal hand-to-hand combat.

The recruits are forced to master their emotions under extreme pressure - from a scary backwards dive at night to an illusion jump. And, to their shock, the mole in their midst is revealed.

The recruits face a forward abseil and an arduous beasting by the DS. There's also an extreme water immersion exercise and a team event in a dark network of disused tunnels.

The recruits face an intense start, with an ambush, a hijack, and a 100-foot abseil off an oil rig.