Cross the Thames southwards over Tower Bridge and you will find yourself in Bermondsey, a landscape of terraced houses, corner shops and red brick Victorian pubs, with high-rise flats looming on the horizon.

Spa School, built in 1896, stands in a quiet side-road - an old London School Board building, now looking somewhat the worse for wear, and not enhanced by its concrete surroundings. Go round to the back, though, and you are in a different world. Where five years ago there was only an expanse of tarmac playground with a solitary climbing frame, a garden is now taking shape. There is the soothing sound of water from a stream that trickles down a gentle grassed incline into a pool, with a wooden deck at one end. Railway sleepers are waiting to be made into raised beds, and the high enclosing fences will soon be covered with climbing plants to create a feeling of safety and containment.

Like the garden, Spa School itself is evolving. Reorganisation in the 1980s turned it from a primary school into a secondary school for pupils with special needs, and in 1995 a centre was set up within the school for eight students with a primary diagnosis of autism. Gradually the number of autistic pupils grew, and last year it was agreed that Spa should become a specialist school for pupils with autistic spectrum disorders, a gradual process of changes to the building that will be completed by 2003.

Autism is a bewildering condition that manifests itself in as many different ways as there are people with it, though all have the same basic impairments to varying degrees. Autistic people find it hard to make connections between themselves and the world, to read the subtle, unspoken signals that help us to understand a situation. Their thinking tends to be rigid, and they cannot easily make jumps of imagination - “Stop and sit down” to an autistic pupil may mean precisely that - an order to sit down on the spot instead of going to a chair.

One autistic author, Temple Grandin, has likened this terrifying and unpredictable world to being locked in a room and chased by a tiger. It is a place where anything that calms and reassures is important: familiar routines, soothing sounds, places of sanctuary where you feel safe and contained.

There had always been a tiny, enclosed garden area at the back of the school and staff noticed that autistic pupils tended to go there during breaks, rather than into the main playground. But the idea of creating a bigger garden was initially sparked at a conference attended by the school bursar, Paul Charter, arranged by the charitable organisation Learning Through Landscapes.

Spa pupils were asked to draw and describe their ideal surroundings, and an inspiring picture emerged of somewhere safe and quiet, a natural environment with grass and trees, a pool and running water. “The sound of water,” says Annie Etherington, head of the department for students with autistic spectrum disorders, “immediately helps people relax.”

She cites the moving example of one particularly disturbed and unhappy autistic pupil who was injuring himself and in need of constant attention. On an outing to a local park with a water feature he immediately became calm and sat alone, drawing the trees.

First, however, there was the daunting prospect of removing hundreds of square feet of tarmac. Paul Charter approached Tarmac plc, which agreed to break up and cart away the central section of the huge playground and lay subsoil free of charge. The construction of a stream and pond was paid for by a grant of pound;3,000 from Barclays New Futures project, and an additional pound;2,000 from a local charity. More money will have to be raised to take the project forward step by step.

Horticulture has always been important at Spa School, and Annie Etherington believes it has a very special meaning for autistic pupils. “We designed a cold frame in design and technology,” she says. “Then we planted potatoes, tended them, harvested them and cooked them. The students were amazed - they thought chips came from the supermarket.

“People with autism tend to live in their heads rather than their bodies. Horticulture connects them to the earth. They can learn only what is taught explicitly and in a garden they can physically feel the earth, hear and see the water, and touch and smell the plants. Gardening sets off a whole string of connections. It shows them that by caring for something they can bring it to life.”

A garden is also a magnet for wildlife. Autistic people often find it easier to relate to birds, animals and fish than to humans and this is a bond the school wants to explore. The deck area is already much used for water-gazing and pond-dipping. Each class will have a bed for growing produce - aside from other benefits, horticulture teaches skills which in the long term can lead to a career.

Pupils have already been practically involved in laying out the garden. Annie Etherington envisages small sanctuary areas, like tiny rooms, created in different ways with rocks and boulders and shady plants. Plants will be chosen for their sensory appeal, and wind chimes may add to the garden’s serenity. It will, she hopes, be a place where pupils can escape the tiger, if only for a while.

* Further information can be obtained from: Learning Through Landscape, South Side Offices, The Law Courts, Winchester SO23 9DL. Tel: 01962 846258. Web: www.ltl. org.uk. Annual membership pound;15.

Information packs on Barclays New Futures: Kallaway Ltd, 2 Portland Road, London W11 4LA. Tel: 020 7221 7883. E-mail: info@kallaway.co.uk