Susanna Reid on documentary about serial killer Joanna Dennehy

Presenter Susanna Reid. Picture: ITV/(C) ITN Productions/Tom Hayward

But Susanna Reid has always made it look effortless as she remains unflappable in the hosting seat of Good Morning Britain.

“You want people to be watching and enjoying and stimulated,” she says enthusiastically.

“It’s such a crucial time for people because Brexit is...we are going to hell in a handcart. It feels like it at the moment.

“It’s fantastic to be able to just put the politicians on the spot, get their views and speak in a really unfettered way to the audience, reflect what they are thinking and ask the difficult questions and also have a laugh about it, as well.”

Their recent guests are as diverse as reality star Gemma Collins and former US vice-presidential candidate Sarah Palin, who helped land the programme its highest ever share of viewers.

“A third of all the people watching television at that time on that Monday morning were watching our interview with Sarah Palin. Isn’t that amazing?” she marvels.

“We haven’t had the Prime Minister or the leader of the Opposition on for good long time, which is a shame and they should come on the programme.

“We like doing the tough stuff, but we also like to keep people entertained in the morning.”

And it’s a good thing 48-year-old Reid does embrace the tough stuff, because her new documentary about one of Britain’s most notorious serial killers could not be much tougher.

The programme, part of ITV’s Crime & Punishment strand, examines the brutal murders committed by Joanna Dennehy in 2013.

Dennehy was just 31 when she was sentenced to spend her whole life in prison after she pleaded guilty to the murders of Lukasz Slaboszewski, 31, Kevin Lee, 48, and John Chapman, 56.

Police launched a nationwide hunt to find her after the bodies were discovered in remote ditches in Cambridgeshire, but she went on to drive 140 miles to Hereford where she repeatedly stabbed two dog walkers.

Five years on from Dennehy’s conviction, Reid speaks to the lead detective, the father of her two children, family members of victims, a man who was present when two of the attacks took place, school friends and experts to paint a picture of how an intelligent and privileged young girl transformed into a dangerous psychopath.

“She doesn’t come a background where you could draw a direct link from something terrible happening to her and her becoming a terrible person,” Reid says.

“She came from a stable, decent family home and was well looked after.

“Her family said butter wouldn’t melt in her mouth.

“When there is not an obvious explanation for why someone has become a serial killer, that makes the detective story more fascinating, doesn’t it?

“It’s not just a tabloid fascination with women who are able to do these things.

“Even the police officer who was investigating the case, when he came across the first body of Kevin Lee in the ditch, his assumption was that the person responsible was going to be a man, because you needed the strength to dispose of the body. But also the humiliating way this poor man had been left in the ditch. He said he never anticipated it was going to be a woman who could do this.

“’How could a women do this?’ is a question that comes up over and over again.

“If you consider that women are far less likely to be responsible as a serial killer, but when they are it’s absolutely shocking. She is only one of three women who got given a whole life sentence in prison.

“The other two are Myra Hindley and Rose West – women with whom we are equally fascinated about how they could be responsible for the worst crimes.

“We live in an equal society, but it is still shocking to us when women are capable of that violence.”

Reid herself became fascinated by Dennehy while working on the programme and describes her as an “abhorrent, horrific, compelling, magnetic character”.

She pauses thoughtfully.

“Her family wrote us a letter about her, saying she was a bookworm when she was at school, she was a good girl, she came from a decent background, happy family, given all the advantages she could possibly want.

“How did she turn into a woman who could brazenly swagger into a police station at the age of 30, boast about the fact she thought five people were dead as a result of her actions, flirt with police officers and show off about being a serial killer?”

For Reid, the details of the crimes, horrific as they are, were not the most affecting part of the film, instead it was the way Dennehy conducted herself.

“We had exclusive access to the full custody tapes, when she’s arrested after being caught on the run and the police know that there are two men fighting for their lives.

“Eventually it emerges that she has already killed three people.

“She is standing in police custody and you would think she would be at least a little bit nervous, at least a little bit concerned for her future and yet she is boasting, ‘Attempted murder and murder is nothing. It’s like going down for a Sunday roast. Easy’.

“She starts flirting with the police officers, trying to charm them and win them over, and you can see they are reluctantly drawn into her web. She’s obviously a really compelling character. She starts playing with her hair.

“Her barrister described her and says he wondered whether he had got the wrong cell, when he eventually goes in to meet her for the first time.

“Normally he would expect someone accused of these awful crimes, who is facing a future in prison never to be released, to be a little bit wary and on the back foot. She wasn’t.

“He said she just seemed to be confident, charismatic, cooperative and she had the type of personality he was drawn to.”

The show is the seventh crime documentary Reid, who is mother to three sons, has made for ITV since 2017, including films about teenager Becky Watts, who was murdered by her step-brother, and the killing of schoolboy Rhys Jones.

“Sometimes I come back from these stories and I am just glad to be in the kitchen with the boys, making tea and doing something ordinary and down to Earth,” she says.

“You don’t want to spend too much of your headspace in the minds of killers. It’s good to be able to do the normal stuff as well.”

Joanna Dennehy: Serial Killer is on ITV at 9pm tonight