The North Water star Colin Farrell details his physical transformation for BBC Two drama

Some fans may hardly recognise Farrell in the disturbing role - he has gained a considerable amount of weight to add to the character's physicality, and he's sporting an unkempt beard and long hair.

These changes are why the True Detective star describes the "unusual" feeling of not being able to take off his costume, but he says it was "a great benefit" to his performance to undertake such a transformation.

"He was a fairly explicitly described character physically [in the book]," Farrell said at a recent press event. "There was a certain kind of power to his body – the way he filled space, the way he moves through space – and a certain brute strength that he had, and the confidence of a man that carries himself with with a keen awareness of that brute strength."

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While many actors have followed complex diet and exercise plans to transform themselves for major roles, Farrell revealed that he kept things relatively simple while preparing to embody Henry Drax.

"I did get fairly strong," he said. "Look, I just put on weight. I just lifted weights and ate, and that's all. Anyone could do it really, although I wouldn’t advise it. And that was it. You couldn't take off the costume.

"I couldn't really step away from the character. I couldn't get out of the costume, he was always with me. It was a great benefit to me because it just meant 24 hours a day, seven days a week for however many weeks we shot, I was constantly inhabiting this physical space that was very different for me."

The North Water is coming soon to BBC Two. Check out more of our Drama coverage or visit our TV Guide to see what's on tonight.