By 2005, Nesbitt had become tired of the formula and threatened to quit unless the structure of the series was changed. He was made a creative consultant and suggested that Murphy keep one undercover role for a full series, instead of changing into a new guise every episode. This new dramatic element to the series was intended to make it a closer representation of real-life undercover work. Alongside his research with former undercover officer Peter Bleksley, Nesbitt hired a personal trainer and grew a handlebar moustache to change Murphy's physical characteristics and tone down the "cheeky chappie" persona that the audience had become accustomed to from his roles. With his trainer, he worked out three times a week, boxing and doing circuits and weights. After the first new episode was broadcast, Sarah Vine wrote in "The Times", "In the past, when attempting a nasty stare or a hard face, Nesbitt has never managed much more than a faintly quizzical look, hilarity forever threatening to break out behind those twinkly Irish eyes. But here, it's different. He genuinely has the air of a man who means business." The refreshed series marked another milestone in Nesbitt's career; he describes it as "a big moment" in his life. "Murphy's Law" was not recommissioned for a sixth series, which Nesbitt attributed to the damage done to the fifth series ratings when it was scheduled opposite the popular ITV drama "Doc Martin".