It’s not often that Sir Trevor McDonald, a veteran of 50 years as a journalist and broadcaster who’s encountered everyone from the Queen to Saddam Hussein, is rendered speechless.

But when he was interviewing American Linda Scarpa, one of the subjects of his latest documentary series Mafia Women, he was taken aback as she showed him her wedding video and matter-of-factly revealed that her hitman dad once asked her permission to kill her husband if he wasn’t treating her right.

“In these programmes you are occasionally confronted by facts which are so extraordinary in their nature,” says Trevor, 77. “How would that conversation go? ‘Let’s have another cup of tea, dear.

I know your husband hasn’t been treating you too well. Want me to bump him off?’ It’s not the kind of chat you hear in south-west London very often.

“Not in the pubs I go to, anyway.”

Linda is the daughter of Italian-born Greg Scarpa Senior, aka The Grim Reaper – a man who stopped counting the number of people he had killed when he passed 50.

She tells Trevor another story about her father “beating almost to death” her teenage best friend from school in New York for smoking pot with her, which shocked him even more.

“The bit that made me cringe more than almost anything else – that a big Mafia boss like that would turn his vengeance on a child,” he says.

“Then bring that child home so his daughter could see what he had done to the boy. I thought that was probably the cruellest thing I had ever heard.”

Despite his horror, Trevor admits the secret world of the Mafia is a subject that fascinated him enough to film a follow-up to his 2015 documentary series, when he interviewed various former high-ranking crime lords who had given evidence against career killers and were living with a price on their head.

He confesses it was hard to shake the feeling that both he and his camera crew might be in jeopardy filming in the US neighbourhoods where many of their subjects committed their crimes.

One former gang member of the Colombo crime family, Anthony Russo, gets so nervous talking on the streets of New York with his formerly estranged daughter Toni, he bolts for cover while still finding the time to tell Toni off for wearing too revealing an outfit.

“I noticed people opening their doors, looking around and then closing them again,” Trevor recalls.

“One guy came and stood about 100 yards away from where we were filming and he wouldn’t leave. I was nervous about who these people were, but it got to Anthony too.

He didn’t want to be there.

These were places where he had been involved in a lot of underhand stuff.

“But that, for us, is the fascination of these films – the complex relationship between these men of violence and their absolute love of their family.

He’d only just rebuilt his relationship with his daughter but there’s this strange juxtaposition between what he was and his concern for his daughter: ‘You don’t go around wearing trousers like that. I’m back to being your father now. Those trousers are showing too much of your backside.’

“Anthony’s girlfriend of six months, Amy, told me a story about Googling and discovering all these murders he’d committed and all this money he’d stolen. And yet she was still there!

"Jesus. I don’t know whether she thought she could somehow change him. I wish I could have that luck with women!”

Most extraordinary is the fact that all these people are prepared to speak to Trevor when they know it could get them killed. Why does he think they took the risk to talk to him?

“I’ve been baffled by this myself,” he says,

“But when I break it down, I think it comes down to one thing – pride.

These people don’t see themselves as we see them. I wouldn’t begin to use the words ‘common criminals’.

They would hate such a description. We see them as part of a criminal enterprise with which you and I would not want to be too close.

"They have an innate pride in what they have done and in being part of this age-old fraternity.”

Trevor was stunned when he learnt that the production company had sent the first series to the men he’d interviewed to watch.

“When they told me, I said: ‘You did what?!’” he laughs. “But they loved it.”

The trust he built, in particular with Michael ‘Mikey Scars’ DiLeonardo – a former member of the Gambino family indicted for two murders, extortion, loan sharking and witness tampering, who turned informant – opened doors again as Trevor and his team were given never-before-granted access to film a Mafia wedding, inside a secret community of fellow informants with their wives and families.

Scars even gave Trevor a chilling gift.

“Mikey Scars is a very strange fellow,” he says.

“I kind of quite like him, although he is one of those who is very good at disguising just how high up in the family he was.

"We had dinner one evening and he had something wrapped in paper which he ceremoniously gave me at the end. I took it back to my room and opened it up.

"It was a tie. I enquired of the guys: ‘What’s this tie all about?’ They told me it was a tie worn by the head of the Gambino family. I thought: ‘Which restaurant am I going to walk into wearing this?!’ I would not want to say I had such a close association with the Gambinos, but he meant it very nicely to me.”

Accommodating though Scars was, Trevor wouldn’t reveal to him what Mikey’s first wife Toni Marie had to say about him when he left her and their son and entered the witness-protection programme with his mistress.

“All I said to him was: ‘She was very frank about you, Mikey,’” he says.

“I left it there. You have to retain some sort of distance. Mikey goes into the witness-protection programme and he takes not his wife but his mistress. That exposed both his son and his wife to vengeance. She was not un-p****d off about this.”

Trevor tells us he’ll return to America for his next show. Perhaps a chat with President Trump?

“I have no interest in interviewing him!” he says. “I’m hoping to do something related to Martin Luther King.

"I never interviewed Barack Obama and I would like to have done that. But you can’t look back at things you could have done. I’ve been terribly lucky to have had more than my fair share of people I have managed to meet.

"I met Nelson Mandela and got to know him reasonably well. I’m happy to rest my laurels on that.”

The Trinidad and Tobago-born presenter pauses and raises an eyebrow.

“But America will be an interesting place to visit,” he says. “Luckily my passport doesn’t say Somalia on it.