By Olga Craig

December 18 is not a date Jean MacColl cares to acknowledge. This year, though frail now at 84, and with fading eyesight, she travelled across London to board a Eurostar train. "As I walked through St Pancras station, suddenly those oh so poignant strains of Fairytale of New York began to play," she says softly.

"Kirsty's lilting voice, Shane's [MacGowan] wonderful growl. It so lifted my spirits. Even though that day is the anniversary of her death, I always feel so comforted by that song, so close to Kirsty. It's like I can reach out and touch her when I hear it."

Mrs MacColl is spending Christmas with her son, Hamish, and her grandsons Jamie, 22, and Louis, 20 - Kirsty's sons - at Hamish's home in the Vendée, France.

It will be a traditional, festive affair and, as always, on Christmas Day the family will play a selection of Kirsty's recordings. They are hoping desperately that Fairytale of New York, the duet between her and the Pogues frontman, will be number one this Christmas, 20 years after it was first released.

"It's always a little sad, of course it is," she concedes. "We all still miss Kirsty so much, especially at this time of year. But we try not to brood. We try to concentrate on celebrating her life."

This year, however, they hope that the new year will bring the news they have fought for since Kirsty, one of the most distinctive singer-songwriters of her generation, was killed by a speedboat off the island of Cozumel in Mexico, in 2000.

They want the truth about exactly who was at the wheel of the 31ft Percalito that ploughed into Kirsty, 41, while she was scuba diving with her sons.

Last week, the Justice for Kirsty campaign was told that the inquiry into Kirsty's death would be reopened after being quietly shelved a few months ago.

Mexico City's Attorney General and its Federal Prosecutor agreed to serve subpoenas by January 15 on two witnesses who, they believe, will help establish whether or not the person driving the speedboat was José Cen Yam, a lowly paid boat hand.

Cen Yam was convicted of culpable homicide for the crime, four years ago, but the family campaign has always suspected that this was not the full story.

There have been allegations that Cen Yam accepted the blame to conceal the role, if any, that the sons of the boat's owner, Guillermo González Nova, or Nova himself, who were on the boat at the time, may have played in the accident. One of those subpoenaed, Gustavo González Fernadez, is Nova's son.

The billionaire, who is head of one of Mexico's largest store and restaurant businesses, Comercial Mexicana, and his sons have always denied that any of them were driving.

In January, however, Fernadez will be required to make a statement. So will the captain of the rescue boat, upon whom the second subpoena will be served, who was never questioned during the initial investigation.

"It's absolutely horrendous that I'm facing the eighth year of fighting for justice for Kirsty," says Mrs MacColl. "Battling to get a fresh and thorough investigation has been tough, but we are really hopeful that now we are on the threshold of knowing who was responsible.

"This hasn't been some vendetta I have been on. I just want the truth, and this renewed inquiry should finally tell us conclusively who was responsible. And, if it doesn't, then I will have to consider approaching the American Court of Human Rights."

In April, Mrs MacColl will publish a book - named Sun on the Water, after the last song Kirsty recorded - about her daughter's life and the campaign for justice.

"I have left the final page blank," she explains, "and I have written to the Mexican government to say I am desperately hoping to be able to fill it before publication with a postscript saying that the truth has finally been revealed."

In the seven years since Kirsty died, the Mexican authorities have dragged their feet over the case. With a newly installed government, however, much more thorough investigations, coupled with those carried out for the MacColls by private detectives, have revealed several more witnesses whose evidence suggests a more complicated story.

Fred Shortland, a family friend who heads the campaign, is even more convinced that the truth will soon be known. "There is a really firm hope that we will have a resolution early next year," he says.

"The weakness in the case has always been that, with the exception of Iván Diaz, the dive master who was with Kirsty in the water, no one else saw Cen Yam jump forward from the back of the boat to the controls just after the accident.

"But now, for the first time, the Mexican authorities have acknowledged that the original investigation was flawed. For the first time, certain individuals will be cross-examined on exactly who was where."

On the day Kirsty died, her mother had just returned to her London home after watching a production of Carmen at the theatre. She was filling her kettle when the telephone rang. "I instantly knew something was wrong when I heard James, Kirsty's boyfriend, and not Kirsty herself.

"He, Kirsty and the boys had flown to Mexico on holiday just a few days before. He was in a dreadful state. He said: 'There has been a terrible accident, Jean, and Kirsty is dead.' I can't remember anything else about that night," she says.

Kirsty and her sons had been diving at a maritime park at the Chankanaab Reef, about 300 metres offshore. The spot was popular with divers, and boats were prohibited from travelling faster than four knots.

As the Percalito powered towards the family, Kirsty pushed her sons to safety but her body was crushed by it. Her limbs were almost torn off and she died instantly. At the time, Louis, then 13, recalled his mother screaming, "look out", as she pushed her sons out of its path.

"I was swimming in Mummy's blood and I heard Jamie shout: 'Where's Mum?' I screamed that she'd been hit and to swim the other way and not look back."

The initial report to the Port Authority stated that Kirsty had been hit in open water, that the boat was travelling at only one knot and that Cen Yam had been steering.

At the subsequent court hearing, in spite of evidence that Cen Yam's job was

maintenance, that he had no licence to drive the boat, or had ever taken the Percalito's helm before, his conviction was upheld.

Though he was sentenced to two years and 10 months in prison, he was allowed, instead, to pay a fine and escaped jail.

"That fine was £61," Mrs MacColl says incredulously. "That was the price of my daughter's life."

Money, though, matters little to the former dancer and actress, who was married to the folk singer Ewan MacColl, Kirsty's father.

At first she paid for investigations from her daughter's estate but, fearing her grandsons would be left penniless, she, along with several of Kirsty's celebrity friends, such as the singers Billy Bragg and Bono, set up the Justice for Kirsty campaign. It has several hundred members.

"So much didn't add up," she says. "If the boat had been going at one knot, it would have gently pushed them aside. Witnesses say it was nearer 18 or 20 knots. Also, we have many witnesses who know that Kirsty and my grandsons were in the maritime park, not in open water as the boat's owner claims."

Her private detectives discovered that Cen Yam had given varying accounts of what happened. According to the evidence of the dive master, he was at the back of the boat.

In his witness statement Diaz said: "After they ran over us, I saw Cen Yam jump forwards from the back of the boat, to the controls. I couldn't see who was at the wheel because the bow was so high out of the water." But, although Diaz wasn't clear about the driver's identity, he did see Nova's two sons at the front, nearest the controls.

Mexican police did interview one of them, Fernadez, but a transcript reveals it to be little more than a polite conversation. Now, however, the campaign has been given assurances that he will face more detailed questioning in the forthcoming inquiry, and the Attorney General has agreed to include questions on exactly who was where at the time of the accident.

"The new government has made it clear that it wants a resolution," Mrs MacColl says. "The difficulty has always been that too many people are frightened to come forward.

"When we asked for Nova and his sons to be subpoenaed before, the police claimed they couldn't find them. Now there seems to be more of a will to listen to all those who witnessed the accident. Before, they ignored anyone who didn't agree with Nova's version."

Although Mrs MacColl has written to Nova, she has never received a reply and he has refused to meet her. Several years ago, the BBC filmed a documentary about Kirsty's death and when its reporters tried to speak to the Novas at their luxurious home, a servant said he couldn't waken them, as they had had a "heavy night".

As she waits to hear if Kirsty's most memorable song will be the number one hit this Christmas, Mrs MacColl acknowledges that she will struggle to stem the tears on Christmas Day. "It's difficult not to give in to the constant pain. I miss Kirsty every day as, of course, do her wonderful sons.

"They affectionately call me 'the warrior' and that's because they know I will never, ever, ever give up until I find out the truth of my daughter's death. Before I die, I will know who was driving that boat."