Speaking to Metro, Threlfall explained that he likes playing his character Frank Gallagher because of his outlandish behaviour.
"He does things I wouldn't do," he said. "He's got a licence to do what other people think of doing. It's not ideal to go round nutting your children, that violence shouldn't be happening, but people understand he's a lost soul and we all have that at some point in our lives.
"He's searching for love and satisfaction in his life and we all want that. He just does it in a chemically and alcoholically influenced way."
Threlfall added that he would like to continue playing Frank if he is offered the opportunity.
"We're doing it until May next year but [Channel 4] seem happy with it," he said. "If someone's foolish enough to give me a job, I'll do it. There's fabulous writing and ideas going on. The viewing figures last year were higher than ever. I'm happy to stay with it and see what they come up with."