I first met Lizzie Pickering 13 years ago when I went to interview her about her two-year-old son Harry. Blonde, beautiful and bright as a button, Harry had been diagnosed six months previously with the rare genetic disease Spinal Muscular Atrophy (SMA).

“We were told it was terminal, incurable and untreatable,” said Lizzie. “It was the most tremendous shock. One moment I had a 17-month-old child who we had taken to the doctor because he wasn’t walking, the next we had the most heartbreaking diagnosis.

“And on top of that we were told that our newborn son, Cameron — who was just six weeks old — had a one-in-four chance of having SMA too, and that we should have him tested immediately.”

At first Lizzie and her husband Hugo felt unable to give permission for this to go ahead.

“I couldn’t bear the thought of Cam having SMA too, but in the end I couldn’t live not knowing,” said Lizzie. “Waiting for the result was the longest two weeks of my life — thankfully he was in the clear.”

Spinal Muscular Atrophy is a devastating muscle-wasting disease and the worst cases do not survive childhood.

After Harry was diagnosed, Lizzie, 44, and Hugo, 47, who live in Lyneham, near Burford, were overwhelmed by the support from relatives and friends, who set up the Harry Fund to help them meet the cost of special equipment for their little boy, including a motorised wheelchair. They also drew on the expertise of The Jennifer Fund, a national charity which supports SMA sufferers and carries out research, aiming to find a cure.

Locally, it was Helen House children’s hospice in East Oxford which offered the Pickerings comfort, support, refuge and occasional respite from the 24-hour-a-day responsibility of caring for their chronically sick child.

With the addition five years ago of a dedicated unit for teenagers and young people, it is now called Helen & Douglas House, and Lizzie is happy to be giving something back to the charity which provided her family with a lifeline.

After years of voluntarily fundraising for the charity, she is now working part-time as their events fundraiser. She used to work in TV and video production for Channel 4, and Hugo works in web-related marketing, so they have been able to draw on their skills and contacts.

Their good friends, TV presenter Jeremy Clarkson and his wife, Francie, who live near Chipping Norton, have been incredibly supportive.

“Eight years ago, Francie suggested that we organise an event together, and that I should choose which charity we supported. I immediately suggested Helen House. We held a power boating day with Honda, and raised £40,000. We were over the moon!”

The next year the Clarksons supported another big fundraiser, a karting day with the backing of Audi, and this brought in a magnificent £150,000.

“Jeremy and Francie have been amazing to Helen and Douglas House, they have been responsible for bringing in £1m over the years. They have been our friends for years, since Harry was born. Their three children are exactly the same ages as our three.

Lizzed added: “They are key to so much for Helen and Douglas House - they have introduced us to all sorts of ways to raise money, and brought in high-profile supporters. When I read bad things about Jeremy in the media I just want to stand up and shout what an amazing man he is and that he is all heart when it comes to children.”

As Harry’s condition worsened, and repeated chest infections made him weaker and weaker, the Pickerings decided that they would like to have a third child.

Lizzie explained: “We received genetic counselling - the chances of our child having SMA were one in four, and that applied to either a boy or girl. We knew the risks and the moral and ethical dilemmas, but we had to try. I became pregnant and the baby was tested in the womb. We were in the clear and Emily was born perfectly healthy 11 years ago.”

Helen House was at the heart of the Pickerings’ life when Harry was alive, and continues to be so through Lizzie’s job. And Hugo supports pioneering research into finding a cure for SMA as trustee of the Spinal Muscular Atrophy Trust.

“We have to raise £4.5m every year to keep Helen & Douglas House running,” said Lizzie. “For many years, fundraising relied on our wonderful volunteers, but with the opening of Douglas House, it has to be run like a business - we realised we had to have a professional fundraising team, because we cannot risk having to close beds.

“Since I was already voluntarily organising one fundraising event each year, with the Clarksons, the hospice asked me to come on board - and I absolutely love it.”

Lizzie said that, far from it reminding her of her loss, it is a totally positive experience: “I use my personal knowledge of Helen & Douglas House to emphasise the need for this wonderful place, which helped us so much when Harry was alive. I feel that Harry is always with me and that he is still working very hard for the charity. I still get a buzz when I go through the doors of the hospice and I love taking people round. It is not depressing in any way - unutterably sad, but never depressing.”

But she admitted she does sometimes get ‘burnt out’.

“It is very hard in November, around the time Harry died,” she explained. “I was involved this November in organising Life!, a big art event in aid of Helen & Douglas, which raised an amazing £70,000. Having worked flat out, now it is over I am taking time over Christmas to recharge the batteries because we have big events lined up in February, March and May.”

Very popular, and a big fundraiser, is the annual comedy show Childish Things, co-organised by Lizzie at Oxford’s New Theatre.

“We have attracted performers like Jimmy Carr, Jo Brand, Bill Bailey and Patrick Kielty in the past, and we are sold out months in advance,” said Lizzie. “It’s a wonderful event. This year, we have Rob Bryden taking part. Both he and Jimmy Carr have been to Helen & Douglas to look round and meet the children and this kind of support is so important to us.”

Cam is now 14 and, says Lizzie, has strong memories of his elder brother.

“Never under-estimate the trauma and suffering of young children,” she stressed. “Cam remembers vividly the day Harry died. A family friend took him to a playground to try to lighten things, and she persuaded us to go too. We were completely shell-shocked, but Cam remembers every bit of the trip.

“He also remembers when, aged three, he had to run and get the machinery and nebulizer if Harry stopped breathing when I was home alone with both of them. I had to pump Harry’s chest while Cam sprang into action. It’s amazing that a three-year-old child had such awareness of how serious it all was.

“Emily was just two when Harry died, and I think she feels she missed out on knowing him. But we have photos of him all round the house and we talk about him all the time.”

Helen & Douglas House provides professional care and support to 250 children, young adults and their families every year, but Lizzie says there are lots more families eligible to use the hospice, but find it difficult to make that first move.

“When we first went to Helen House, we were both suffering from severe sleep deprivation,” explained Lizzie. “Caring for Harry was a 24-hours-a-day job. Our GP suggested we went there, but we found it hard to go through the doors - we didn’t know what we would find.

“What we did find was laughter, colour and life. This place gave us a lifeline when we were desperate. They let us have an annual holiday with Cam and Emily, while Harry was looked after, and long weekend respite breaks for more than four years. The whole family could stay in one of the flats there while Harry was receiving brilliant care.”

Lizzie concluded: “Helen & Douglas House, the children, young adults and families all demonstrate the incredible strength of the human spirit. Coming here is inspirational every day.”