21 new recruits embark upon a recreation of the brutal SAS selection process, starting with an ambush, a hijack and a 100-foot abseil, which proves to be the toughest course to date.

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 must master their emotions under extreme pressure - from a scary backwards dive at night to an illusion jump. There is a further shock as the mole in their midst is revealed.

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 on the run across the punishing landscape, pursued by a military-trained hunter force, in a real life game of cat and mouse where only the strongest will make it through.

The remaining recruits face the final stages which consist of an interrogation and a brutal sickener. They must prove that they have both the mental and physical strength to complete the process.

Led by Ant Middleton, 25 men and women - including an ex-SAS operator working as a mole - face the latest intense course, beginning with a swim to a remote Scottish island.

The recruits are pushed to control their aggression, as they're trained with guns and take part in hand-to-hand combat, in an episode exploring loss, loyalty and self-control.

The recruits take on the intense close-combat murderball and surf immersion - a notorious water beasting that simulates water torture.

The recruits' grit is tested as Jay's undercover status is revealed and he launches a brutal beasting to expose the weakest in the group.

The recruits are stalked across the Scottish Highlands by a military-trained hunter force, before facing extreme interrogation on limited sleep and rations. Who will crack?

The last six recruits face deep interrogation and a day of sickeners, including `drownproofing' - simulated drowning. Only the physically and mentally elite will make it through.

For the first time, female recruits join the selection process. In a dramatic opening episode, the women fall behind the men; how many will make it through to the end of the first stage?

The remaining male and female recruits face gruelling challenges designed to test their mental and physical strength, including a 200-foot forward abseil and an infamous boxing task

With the conditions deteriorating, the recruits must negotiate beastings in the snow and a night out in a blizzard 3000 metres above sea level, while the DS increase the psychological pressure on them.

This episode is about trust. The recruits are teamed up in pairs, then take a free-falling abseil into a rocky gorge and plunge into freezing water, with their partners responsible for saving them.

The remaining recruits must cross a 200-metre gorge, swim beneath the ice on a frozen lake and navigate a perilous valley at night, while trying to avoid capture by a local hunter force and their dogs.

The remaining men and women's final challenge is also the most psychologically demanding: resistance to interrogation, as they're subjected to stress positions, white noise and relentless grilling.

From the start, the recruits face a series of extreme, high-pressure tasks, including jumping from a moving helicopter into a lake and crawling across a vast canyon on a tightrope

The recruits must abseil 200 feet off a dam and climb a mountain in blistering heat with 40lbs on their backs

The recruits race each other across sand dunes in the Sahara and must cross a valley at night while avoiding hunter teams who are tracking them with dogs

The recruits must dive 10 metres into a reservoir - backwards, and blindfolded. And then they're captured and intensely interrogated in an extreme test of mental resilience, trust and moral judgement.

Eighteen recruits down, seven to go... and it's the most demanding final phase the instructors have ever designed. Some recruits have to give up, others are culled. Will any of them pass the course?

The recruits face a terrifying bridge leap before they can find their base. The jungle environment, altitude and insects take their toll, and the DS give special attention to two volatile individuals.

Chief Instructor Ant and his elite team test whether the remaining recruits can control their aggression, with a brutal game of murderball and the fearsome non-stop 'sickener' exercises

The remaining recruits' trustworthiness is tested, as the directing staff sow distrust among them and ask them to identify their least trustworthy teammates, before a forward abseil trust exercise

The directing staff apply pressure to the last eight recruits, exposing hidden personality traits before sending them into a gruelling 12-hour jungle mission high in the Andes

In the final episode, the remaining recruits undergo the most psychologically demanding 24 hours of the course: the resistance to interrogation phase, as they are abducted and intensively interrogated

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?