Decades of rivalry are tested as 14 British and Australian celebs take on an SAS selection course. First up is an underwater drill and it's Brits vs Aussies in hand-to-hand combat.

Phase two pushes recruits to breaking point with psych tests, split-second life and death decisions, mud tunnels and a brutal beasting that forces one of the celebs out.

A perilous ladder escape, 15 metres up, is followed by a scorching ammo mission up the side of a mountain, as one recruit's lack of leadership is exposed for all to see.

Brutal tasks, searing moral tests and a slip of a celebrity tongue pile on the pressure and push several recruits to exit point as some of them walk away broken.

The recruits are hurled into an explosive task, hauling 200kg of kit under fire. A failed rescue mission, a brutal task and rising pressure test group bonds as armbands are stripped and emotions laid bare.

High-wire terror 165 feet above a canyon, brutal combat with the notorious Redman, and emotional death letters home push some of the recruits' composure off the graph.

The emotional strain is cranked even higher as the escape and evasion challenge leads the remaining celebs into the darkness, where they must somehow navigate through the unknown.

It's the final countdown as the recruits face their last but toughest challenge: a 12-hour interrogation including hoods, stress and extreme noise. Only the strongest survive.