The recruits' first task is an unexpected one: writing an essay about themselves. Then they face an eight-mile combat fitness test while their essays are dissected for an insight into their character.

The remaining recruits must choose their weakest colleagues, who then lead the next exercise. And there's the 'Sickener': a series of physical challenges that won't end until five recruits give up.

The directing staff test the remaining recruits' resistance to fear, with mind games and an intimidating challenge to dive backwards from a cliff into the freezing sea 12 metres below.

The directing staff have to whittle the group down to the six they think may have what it takes to complete the final stage: a punishing 72-hour cat-and-mouse chase across challenging terrain.

The remaining recruits each face the final, notoriously gruelling stage of selection alone: 24 hours of interrogation. Do any of them have what it takes to succeed in the Special Forces?