Hannah Mayne was a sensitive, artistic child, often moved to stand up for others being bullied at school and always helpful to her parents.

But as she grew into a teenager, that fragility took her on a painful path from which she has never recovered. Turned off from the world around her she submerged herself in a world of drugs and alcohol, dragging her family into their own personal hell.

Here, her mother Kate explains how three years ago her world changed forever.

Kate Mayne jumps every time the phone rings, unsure if it will be the owner of some historic home she is due to decorate or a drug dealer demanding payment from her daughter.

Taking time away from her job as an interior designer, she sits surrounded by photographs of her beautiful eldest girl taken only three years ago, her face healthy and smiling.

As a student at Bishop Luffa school in Chichester, Hannah Mayne had excelled at art and maths. Her mother remembers being offered money at a homes exhibition for a painting of an elephant which displayed her nine-year-old's precocious talent.

But Hannah suffered from severely low self-esteem and was "an unhappy child, not cuddly". The family moved home six times before her teens and she found it difficult to cope with the change.

When she hit her teenage years she chose not to cope at all.

Kate recalls being worried back then. She said: "It was binge-drinking, and I didn't like it, but it was the truanting which worried us most.

"I used to try everything with the school, constantly meeting with the truancy team and headteacher and we would try to come up with new ideas like work experience instead of full-time schooling.

"The school were very supportive but Hannah was determined to self-destruct.

We tried to set boundaries but it was hard to help her."

Hannah finally left the family home to stay with her aunt in Monmouthshire for about eight months.

But ironically, it was here, in a tiny Welsh mountain village that she had her first taste of heroin. She didn't like it that time, but having already become a cannabis and cocaine user, her addictive personality would soon lead her back to its destructive hold.

She returned to her parents' house, now in Brighton, in spring 2004 and at first things seems to take a happy turn.

Hannah got a summer job in a seafront café and worked hard doing long hours and making a good set of friends.

The seasonal job ended in September 2004 and she could not find another employer who would put up with her drinking too much and refusing to get out of bed. Kate and her husband hoped that paying rent might force her to act responsibly and Hannah moved into a bedsit in spring 2005, aged 18.

But instead Hannah descended into Brighton's darker side - one of nightclub loos filled with drug pushers and one which pushed her into the vice-like grip of heroin addiction.

Kate and her husband were informed of the extent of their daughter's problem by Hannah herself.

One Sunday morning in October 2004 she burst into their family church service at St Nicholas Church in Brighton in front of a stunned congregation.

Kate said: "She said her life was in a dreadful mess and wanted us to help her. It was rather dramatic.

"We knew there were problems but we didn't know the extent. The congregation were very understanding."

That church service is one of several perverse juxtapositions Kate deals with, juggling her middle-class professional lifestyle with the seedy world of drugs.

Her home is impeccably decorated with fine furnishings and fresh flowers - her bathroom stocked up with Molton Brown toiletries and looking out on to a large planned garden.

The irony is not lost on her. She recalls her last birthday. She said: "Three of us were having a lovely lunch for my birthday in a restaurant when I got a call from Hannah because she owed a dealer money.

"She was hysterical because she couldn't leave her hostel so we, and a huge bunch of birthday tulips, got a taxi to the hostel in New Steine Mews and were escorted to a cashpoint by the drug dealer's girlfriend.

"The room was awful, strewn with litter and plates of decaying food and it stank of tobacco."

The most distressing time she remembers was watching her daughter inject heroin.

She said: "I had to be there to make sure she didn't overdose but it was very distressing.

"I was supposed to be at my other daughter's charity fashion show so I left this squalid bedsit, seeing my frail, fragile eldest daughter and went to watch my youngest, beautiful and healthy and altruistic, raising money for an Aids charity with her friends."

Hannah's younger sister is heart-broken and remains very close to her 19-year-old sibling. Thankfully having seen the damaging effects of drugs so closely, she is appalled rather than impressed by the glamorisation of drugs in the media.

Kate said: "There's a sector of society that will try to glamorise it and say it's artistic like Pete Doherty and Kate Moss, but it's not like that at all.

"It's squalid and degrading and it ruins everybody's lives. We don't have a life anymore, we just function from day to day and just react to events as they happen.

"Working hard to have a comfortable living and a lovely home means nothing when you have to deal with what we do.

"You go to bed and think, Well that was today and I'm tired', and then you wake up with no sense of enjoyment, just hoping nothing will happen.

"I have seen the underbelly of Brighton in all its degradation. I can't walk into Brighton now without spotting the heroin addicts. I know what to look for and I know their sad stories and it's very depressing."

Asked how easy it is to buy heroin in Brighton Kate just laughs.

"I could ring them now and meet them in a cemetery in five minutes. I have a number in my mobile phone," she said. "I overhear conversations in hostels and it's predominantly where to get drugs from, who to contact, how much they have taken, what it's like, whose veins have collapsed and who has had veins removed. It's surreal."

But although she believes Brighton is part of the problem, filled as it is with a deeply embedded hard drugs industry, she still loves the city she made home three years ago.

She said: "It's the best and worst of places. There are two sides to Brighton. It's bad because there are drugs here but good because people are understanding and supportive.

"If I had still been in a small Hampshire town it would have been harder, it is non-judgmental here.

"Everyone has said, What can we do to help?'. I haven't felt any blame directed at me and people have said, it could be us anyway'.

"I want to puncture this myth that it doesn't happen to a middle-class family."

But most families will not have had to endure the pain of being burgled three times by their daughter and her partner before welcoming them both into their home for Christmas dinner.

They will not have come home to find their daughter shivering and wet in a dirty hooded top on their doorstep with hair so lank and eyes so dead, that her desperation was etched on her drug-ravaged face.

Though it may be hard to believe, sometimes, Kate says, Hannah can be a perfect daughter - an excellent cook who helps with the ironing and quite contrite.

But at other times she has been aggressive and violent, trying to attack her sister and once lunging at her mother with a glass.

She has attempted to get help and was on the heroin substitute methadone for a while.

But in her sensitive state she is easily set back and when a friend died of an overdose last February she decided to lose herself once more in heroin and crack.

A few weeks ago she told her mother she was going to kill herself - first deciding to throw herself from a multi-storey car park before planning to inject air into her veins.

Since then, life has been a constant worry and Kate waits on edge for the next phone call.

She said: "If I see her I worry because she's drugged and ill but if I don't I worry because I wonder what's happened. My life is constant with worry and I can't relax.

"I've got a very real fear she'll overdose or be killed. I used to rehearse her funeral in my head every night. I'd wake up having done the whole thing from start to finish and be absolutely distraught.

"I've got good family and friends and I see a counsellor once a week but I avoid pills - occasionally I'll take something to help me sleep but I don't like drugs and never have."

Kate, her husband and daughter occasionally get a holiday when good friends act as respite carers for Hannah.

But for now there is no end in sight. Hannah is waiting to go into rehab once more but she faces an uphill battle to stay on methadone for long enough to be admitted.

Kate's ambitions are much more mundane for now. She said: "The best thing would be to have just one normal day. One day I can plan from beginning to end without the phone ringing and having to attend a crisis. That would be wonderful."

Read part two of Kate and Hannah Mayne's harrowing story tomorrow.

Have you been affected by drugs? What do you think of the scale of the drugs problem in Sussex? Leave your comments below.