Lucy Todd was overjoyed when she heard she had made the shortlist of a national photographic competition.

But as an agoraphobic, she knew there was no way she could make it to the prize-giving ceremony at the Natural History Museum in London last month and had to send her parents in her place.

While they collected her certificate and posed for pictures with the host, Blue Peter vet Tricia Mundy, 18-year-old Lucy sat at home and waited for updates by text.

At a time when her friends have been expanding their horizons - heading off to university or gap years abroad - Lucy's world has been steadily shrinking.

Her crippling phobia means ordinary teenage pursuits like a trip to Topshop or a night out clubbing are unthinkable.

She can travel only a short distance from her home in West Sussex before panic sets in, and entering any other building is impossible.

"My heart races, I get hot, the room begins to spin and my legs feel like they can't hold me," she said.

It's a flight or fight response, and once I get to a certain point there's no return. I can't calm down and the only thing to do is leave.

"It's never a rational thought process. Sometimes I start thinking the building will fall down, or a hole will open up.

"I also experience derealisation when I feel like things aren't real. It's a very strange thing and it can overwhelm you if you sit thinking about it too much."

Lucy's first panic attack was four years ago during a maths lesson at Davison High School in Worthing.

It was not a particularly stressful lesson and afterwards she put the symptoms down to a fever but then the symptoms returned.

She said: "At first I was only suffering attacks in certain classrooms which were upstairs and I thought it might be something to do with climbing the stairs.

"Then it started happening everywhere - at the supermarkets, in the car, in the cinema - anywhere I was far from home.

"I staggered on through the end of Year 10 and tried to go back after the holidays but I was spending the whole time in the medical room.

"Finally mum said she didn't want to put me through any more, so I started studying at home."

She was able to take part in an innovative pilot scheme run by West Sussex County Council, which enabled her to attend a 'virtual school', communicating with teachers over the internet.

Despite her problems, she racked up seven As and three A*s at GCSE. She had hoped to be well enough to continue her studies at Worthing College, but that proved to be a step too far.

Instead, she persuaded the Open University to give her special dispensation to take courses in biology and photography even though she was two years younger than the usual age of entry.

She spends several hours a day studying alone at the home in Salvington Hill, Worthing, which she shares with her parents Anne and Keith and 29-year-old brother Joe, who are all teachers.

Facebook and email enables her to keep in close contact with her friends but she still feels isolated at times.

She said: "It's a very lonely life. My friends are all off at college in different areas of the country and even when they come home I can't go pubbing and clubbing.

"I used to love going shopping with friends, but I can't. My mum and sister are really good at getting me clothes though and the internet is useful for shopping.

"I love films but it takes forever for them to come out on DVD, which can be annoying."

Getting treatment has been difficult. She had to drop out of cognitive behaviour therapy sessions at Worthing Hospital because the trips to the hospital were so stressful they were making her condition worse.

Now she is trying a complementary therapy called emotional freedom techniques, which claims to unblock trapped emotions through counselling and tapping energy meridian lines in the body.

She is optimistic that one day she will beat her phobia, but finds it difficult to predict when that might be.

"I have no idea of any time spans, so it's difficult to make any plans," she said, "but I'm working on it."