A quarter of a century on, James Bulger’s mum’s grief is never-ending.

As are the four words she can never stop thinking: “I let him go”.

And Denise Fergus remains haunted by the thought her son was calling for her, and she didn’t — she couldn’t — come.

The image of a tiny boy, hand trustingly in that of another child, being led to his death, remains as brutally searing as it did the day James disappeared on February 12, 1993.

A quarter of a century, the grainy CCTV images is as abhorrent as it has been since the moment the world discovered what happened next.

James was just one month away from his third birthday when he was enticed away from his mother, then callously, brutally murdered in a crime that shook a country to its very core.

The pain and second-guessing may dull with time, but they never stop, Denise reveals in her new book, I Let Him Go.

The book, to be released in the UK on January 25, marks the first time Denise has written about her son, their lives before and since, and her grief.

It’s also a way of reclaiming her son, remembering him as far more as the little boy who was murdered.

“Over the years many people have wrote about my son and never even known him. Now you can read my story,” she said via Twitter.

But as much as she celebrates a laughing toddler who lived life at one speed — usually running into the arms of others — the book is haunting, heartbreaking and unflinching,

She can’t stop the thought that springs into her mind still: that James would have called for help, for her. And she couldn’t hear. She didn’t come.

But she has come to realise, ultimately, who is to blame, The Guardian reports. “When you’ve lost a child, you go through stages,” Denise writes. “You blame yourself. You blame others. But at the end of it there are only two people to blame in this, and that’s the two who took him.

“But it did take me a long time to realise that and get my head around it. It wasn’t me that killed James.”

‘THEN HE WAS GONE FOREVER’

Reliving the day James disappeared, Denise writes how difficult it was to walk away from the shopping centre with him still missing.

“I was crying so much I couldn’t breathe. The thought of leaving the shopping centre without him was crushing. I knew that walking away from the place where he had gone missing, without any idea where he now was, meant that things were really bad.

“James had been right by my side and then he was gone forever.”

As the world held its breath, the almost incomprehensible began to emerge.

Grainy CCTV footage revealed then 10-year-olds Jon Venables and Robert Thompson enticing James towards them as he mum dropped his hand to pay for sausages.

They led the tiny, trusting toddler out of the shopping centre, about 3km through traffic, along a canal towpath, then battered him with a 100kg iron bar.

They poured modelling paint into his eyes. Stoned him and clubbed him with half-bricks.

They left him on a railway track to be run over by a train.

In November 1993, the pair, by now both 11, were found guilty of abducting and murdering James after a trial at Preston Crown Court.

The verdict made them the youngest convicted murderers in Britain for 250 years and they were detained in youth custody indefinitely.

They spent seven years receiving costly treatment and rehabilitation at secure units before being released in 2001 — with new identities to make a new start in the world.

They were 18 when the government announced their release and barred the British media from disclosing their identities, despite public appeals to keep them in jail.

To say there was outrage is an understatement.

‘PARALYSED WITH HATRED’

She has zero time for those who make excuses for James’s killers, but Denise did condemn calls for vigilante acts to exact revenge at the time.

Which is not to say she wasn’t angry, and didn’t want the justice system to do it’s job.

“Any decent person who makes a mistake should be given the chance to make amends”, she wrote. “But that doesn’t apply to Venables and Thompson: they aren’t decent people who live by the same morals we do.”

In 2001, when the pair was released, complete with new identities, her own anger boiled over.

She smashed up the bedroom. “I couldn’t deliver and the guilt swamped me,” she wrote.

In 2004 she told News of the World she had tracked Thompson down, intending to confront him. But “paralysed with hatred”, she couldn’t do it.

She stared, silent, as he wandered down the street. But she also wanted to know where Venables was.

Right now she — and the wider public — know exactly where he is: back behind bars, charged with possessing indecent pictures of children. There is fresh outcry — not just about the charges — but over the fact his identity will again be protected as he faces the courts.

James’s father, Ralph, called for him to be stripped of his anonymity as he was thrown back behind bars.

‘I DON’T EVEN LIKE SAYING THEIR NAMES’

Denise will never forgive, but the blinding anger has receded.

“I haven’t got the energy for it any more,” she told The Guardian. “I don’t give them the time of day any more. I don’t think about them, I don’t even like saying their names.”

In the book she details her horror and shock as she learned the age of James’s killers and her disgust when she realised Thompson had laid flowers on the train track where James’s body was found.

She writes: “Thompson lived in Walton, not far from the murder scene, with his mum and two younger brothers. The arresting officer ended up speaking to Thompson’s seven-year-old brother.

“He said he knew about the murder, so much so that he and Thompson had been down to put flowers by the tracks.

“I remember hearing that and wondering if we were making a terrible mistake. I mean, what adult could be that conniving if they had murdered someone, let alone a child behaving so cynically?”

‘WHAT COULD WE POSSIBLY SAY THAT WOULD MAKE IT BETTER?’

After James’s death, Denise thought about killing herself “often and in great detail”, she reveals.

Certainly his murder killed her marriage, as she and then-husband, Ralph, reeled in shock and grief, “not really” able to talk about what had happened.

“He was finding his solace in drink, I was finding mine in silence,” she wrote.

“A distance set in between us that just got bigger as time passed — it was like rot setting in. “Ralph had never been a man to talk about his feelings and it was particularly hard in awful circumstances such as this.

“What could we possibly say to each other that could make it any better?”

STILL FIGHTING

Even before it has been released, the book has seen renewed calls for a public inquiry into the James Bulger murder case.

A petition calling for that has received more than 7000 signatures.

Denise has supported it, and called for people to sign it, via Twitter.

“As I have always said — I will continue to fight for justice for my son James — please support the new petition for a public inquiry #JusticeForJames,” she said in a Twitter post.

“I will never stop fighting for my little boy.”

I Let Him Go will be published on January 25, with a portion of the proceeds going to the James Bulger Memorial Trust.