The air raid siren echoes through the warren of corridors known as trenches, deep under a grassy bank at the rear of the school.

It is dank and cold. The drone of bombers can be heard in the background.

The sounds are coming from a tape deck but give a taste of what life was like during the war.

Whitehawk Primary in Brighton was a senior school at the time.

As many as 200 pupils would often sit huddled along benches lining the trenches. The school was never hit but bombs landed close by.

Spitfires and Hurricanes could be seen high above the school as they engaged in dogfights with the enemy, sometimes several times a day during the Battle of Britain.

Entries from a diary kept by the school in 1940 bring home the drama.

July 14: "This morning, at 6am, a solitary German raider dropped bombs in the district about three-quarters of a mile from the school. No damage done to school but house property was affected."

August 8: "First air raid warning during school hours. 9.30am, children spent over 30 minutes in the trenches."

September 24: "12.05pm German bomber chased over Whitehawk Valley by Spitfire. Heavy machinegun fire."

September 30: "Milk and sweets in the trenches. Carried on work, reading and writing."

Dudley Button, the school's property manager and a former policeman, was a small boy during the Blitz. He remembers seeing house windows blown out during the bombing of Brighton and wants former Whitehawk pupils or their families to come forward and tell more tales.

Tin hats and gas masks are on display but he wants real-life stories to add atmosphere to the museum.

It will be open for visits by other schools and Mr Button hopes the museum will be unveiled in time for the school's fair on June 12.

Work on clearing rubbish, painting iron supports, opening old vent shafts and replacing rotten benches is being carried out unpaid by offenders under the direction of the Sussex branch of the National Probation Service.

Colin Molloy, 19 and from Brighton, was sentenced to 180 hours' community punishment for burglary.

He said: "I don't enjoy the work really. I'd rather be in a job earning money but I like the idea of giving something back to the community."

Kasru Miah, a 23-year-old Londoner, was given 100 hours for GBH. He said: "I quite enjoy the work. It's a bit of fun and it beats prison."

Community punishment project manager Veronica Bower-Feek said the work was anything but a soft touch.

She said: "The days of offenders standing around painting fences are gone.

"Two unacceptable absences from the project or they don't do the work we set them and they can be sent back to court. And there's no time off for good behaviour. They are well aware of the ramifications and they are responding well."

Probation Service communications manager Anit Chatrath said: "The project will mean an important piece of Brighton's past will again come to life in a historic and educational sense.

"An external consultant who surveyed the site before work began referred to shelters as 'a remarkable piece of 20th Century history'.

"Offenders have undertaken much of this restoration underground in cramped conditions."

Mr Chatrath said the shelter project gave value for money, adding: "The average cost for an offender on a community project is £1,521 a year. It costs about £35,000 a year to keep an offender in prison."