In his upcoming ITV drama Safe House - in which he plays an ex-copper who runs a police protection refuge in Cumbria - his character is often shown swimming in the freezing cold waters of the Lake District in the middle of winter.
And the heroic actor did all the swimming himself – "no extras, no body doubles no nothing" as ITV drama boss Steve November admiringly puts it.
Adds Eccleston: "It's all part of my mid-life crisis. I thought for my character, who has been through trauma, exercise would act as a stress relief. It was something I would always do during periods of unemployment."
Still, there were some consolations for the actor.
"It was lovely filming in the wild – we picked blackberries and we found a great pub called The Old Bull in Coniston," he says. However he did admit that it rained a lot on set.
"Our families came up and it rained and they ate mint cake and went home," he added with a laugh.
Inspired by the story of a real couple, the four-part drama begins when Eccleston's character Robert and his teacher wife Katy (Marsha Thomason) are asked by close friend and police officer Mark (Paterson Joseph), to turn their remote Lake District B&B into a safe house for protected witnesses and crime victims.
Their decision to say yes means Robert revisiting the memory of a tragedy from his time as a policeman when a witness he was protecting was shot and killed.
The first family that come under Katy and Robert's care also cause the couple a few problems...