Critical: Sky's new series is not for the squeamish

New Sky series 'Critical', Gerard Gilbert views an early cut of the drama set in real time in a trauma centre

Smooth operators: Claire Skinner, Prasanna Puwanarajah and Catherine Walker in 'Critical'

Britain's newest hospital is situated on the western fringes of the M25 in Surrey, with gleaming medical equipment more likely to be found in Saudi Arabia than in our own NHS, walls whiter than a minimalist's wet dreams, and a reception desk more starship Enterprise than Holby General. Unfortunately, for those living in the vicinity, this football field-sized facility is a fake. The bustle is that of a film set, not a trauma centre, and all the doctors and nurses are actors – except for a full-time medical consultant making sure the procedures in Sky1's new real-time drama Critical are correct.

"It's about showing an actor how to hold a particular instrument… the fine detail of surgical technique", explains Critical's writer-creator, Jed Mercurio. The former hospital physician is responsible for the hit BBC2 thriller Line of Duty but also, more pertinently, for the ground-breaking 1994 series Cardiac Arrest and 2004's Bodies, with its scalpel-sharp incision of health-service politics.

Critical is also ground-breaking, but in a different way. Its trauma centre is partly modelled on the Queen Elizabeth Hospital's in Birmingham ("most of the NHS is not like this," admits Mercurio), and the action takes place in real time – during the "golden" hour after the ambulance or helicopter deposits the patient at its doors. A clock ticks down the minutes in the style of the Kiefer Sutherland spy drama 24.

"I was participating in a documentary that Mark Lawson did for Radio 4 and he asked me how a medical drama could be as realistic as possible," says Mercurio when I meet him on set. "I couldn't really answer that at the time, but it set me thinking.

"And then when I went into Sky, who I knew were looking for a medical drama, I explained I had this idea of doing something that was in real time so you don't miss out all the bits, so you have to show everything. But how do you create a framework for that so that it's exciting?"

All the bits… showing everything… Critical, more than most medical dramas, is not for the squeamish. Mercurio made it even harder on viewers by having the patient, whose backstory is such a crucial element in traditional shows such as Casualty, as simply a convulsing amalgamation of gaping wounds, mashed up bones and internal organs, often without a name. "We don't go too much into the patient's social history," says Mercurio with some understatement. "We don't go down the road where the medical condition is actually just a gateway into psychological or social issues."

The other staple of the medical drama, the personal and romantic relationships of the doctors and nurses, are also not central. We catch intriguing snippets – the senior consultant, played by Claire Skinner, is obviously undergoing a professional crisis – and these will no doubt build into a fuller picture over the 12-episode story arc. But week by week we see only what might realistically be glimpsed during a one-hour medical intervention.

It's more a matter of actors such as Lennie James and Neve McIntosh barking medical jargon about "uncontrolled intrathoracic haemorrhages" and "severely hypertensive radial pulses". The essential butchery of surgery is brought home in a scene where a rookie trauma doctor (played by Kimberley Nixon from, aptly enough, Fresh Meat) is ordered to "stick her finger" in a patient's heart. Anyone hoping for something akin to ER's Doug Ross and Carol Hathaway making eyes at each other above their surgical masks will have to look elsewhere.

"There is a bit of that," admits Mercurio. "There's a strong relationship between the two leads – between Lennie James and Catherine Walker, who play the trauma consultant and the trauma registrar – but the way we play it out is different as each episode is about the struggle to save someone's life. They don't have the time to go off for a coffee, or go home together."

Critical shouldn't work, but in its own brave new way it does. Despite early misgivings, I was intrigued by the end of the first episode. As Chris Hall, the producer, says: "This is partly a detective story…what's wrong with the body?" Or bodies in the case of the scene I watch being filmed, a car crash with multiple victims.

One of these is on a trolley in front of me now, his chest sliced open to reveal his heart. It's a life-sized dummy, with a prosthetic heart, and an exact replica of one of the show's many "supporting artists". "The commitment of the extras is immense and their names appear on the end credits," says Hall. "One burns victim had four hours of make-up, and they come here day after day lying on their back."

The leading actors did a trauma course at St George's Hospital in London, and Mercurio drew on his own experiences as a trauma doctor at Birmingham Aston Hospital more than 20 years ago. "I've had to get up to speed on some things," he says. "I used my medical contacts to shadow mates who now work in trauma."

The realism extends to the gallows humour of some of the trauma team, a cynical side of medical life that shocked viewers in 1994 when Mercurio portrayed junior doctors in Cardiac Arrest, and something that still differentiates his drama from documentary series like Channel 4's feted 24 Hours in A&E.

"I've seen plenty of documentaries about hospitals and they're quite selective about what they show," he says, before slipping off to conduct a casting session for his next project – a new BBC adaptation of DH Lawrence's Lady Chatterley's Lover. "Medical people play up to the cameras, and none of those documentaries have shown what I think is the real way people behave in hospitals behind closed doors."

'Critical' begins on Tuesday 24 February at 9pm on Sky1