Gone Fishing: Bob Mortimer and Paul Whitehouse on the return of their hit show

“I caught a fish, and while I was trying to land it, Bob fell over in the mud. And as he fell over, he took me out as well. So the pair of us was sort of lying in the mud.

“I remember thinking in those few seconds, ‘The angling world is going to hate us, but this is funny’.”

Four years on, the wholesome and hilarious BBC Two series is about to return for its fifth series – and those jokes, japes and silliness are intrinsically part of the programme’s DNA.

For the uninitiated, Gone Fishing follows comedy legends Bob Mortimer and Paul Whitehouse as they fish some of the UK’s most beautiful waters, talking about life, health, angling and nature with a healthy dose of slapstick silliness.

I catch up with the pair as they cast a line for perch on the grassy banks of the Thames, a river that they both fondly remember fishing when they were young, as they reflect on the success of Gone Fishing and reveal what’s to come in its fifth series.

Their faces often feature cheeky grins, their conversations peppered with sincere laughter, but considering the very serious origins of the series, it’s clear that their relationship is about far more than just fooling around.

“We’ve known each other for over 30 years now, and we’ve always threatened to go fishing,” explains Harry & Paul and The Fast Show’s Whitehouse, 64.

“Always threatened,” Mortimer, 63, repeats. “Never managed,” returns Whitehouse.

It took decades – and Mortimer undergoing triple heart bypass surgery – for the pair to actually get the tackle box out, as Whitehouse, who’d had his own heart health problems, “came along and ruined (Mortimer’s) peace and quiet” to get him out of the house and help his mental health after his operation.

“I’d already had some stents, but Bob got there and was competitive as ever, outdid me in the heart disease stakes,” says Whitehouse.

“You thought you were going in for stents,” he adds, then adopting the voice of a gameshow host: “But tonight, Bobby Mortimer, your lucky night, let’s play: bypass!

“It’s very traumatic, open heart surgery, isn’t it Bob?”

“It’s always easier not to go out,” Mortimer says of life after the operation.

“You’re so scared of using your body after the heart stuff. But it’s the very best thing for you. So I’m very grateful for that.”

It’s been seven years since his surgery, and four since the pair turned their hobby into a television series. While Gone Fishing was never intended to be a show that particularly discussed men’s health, Mortimer says he found that “unbelievable to us, people had really enjoyed that discussion”.

Mortimer & Whitehouse: Gone Fishing returns to BBC Two at 9pm on Friday, September 9.