THE distinctive purple blazer has been a familiar sight on the streets of Sidcup for more than 50 years.

It belongs, of course, to Chislehurst and Sidcup Grammar School one of the best-known schools in the borough.

A book, Past Purple, written by former school master Charles Wells, gives a fascinating insight into the making of the school's reputation for academic excellence and its transformation from the original fee-paying boys school to the co-educational grammar school of the 21st Century.

It is packed with anecdotes about the staff, many of them distinguished academics, about school life and how changing local and national politics sometimes put the school's very survival on a knife edge.

Some surprising facts emerge about the school, always known affectionately as "Chis and Sid".

At one time, it got more pupils into Oxford and Cambridge on open awards than many of the public schools including Charterhouse and Repton. In 1966/67, 23 boys gained Oxbridge places.

Purple was chosen as the distinctive uniform colour by its first head, Dr McGregor Williams, because his wife wore the colour at their wedding as a sign of mourning after many of the men from their home town of Newport had been killed during a battle on the Somme during the First World War.

In 1938, the school, now Chislehurst and Sidcup County School moved into its first, purpose-built home, considered quite a sensation at the time.

The building, dubbed the "glasshouse" located at Crittalls Corner is now home to Kemnal Technology College.

But its location was also part of "Bomb Alley" during the Second World War. Being so close to both Biggin Hill and London, the boys were used to seeing dog fights between British and German planes in the skies overhead and the school with all its glass windows was extensively damaged.

One old boy who distinguished himself was Michael Carreck. He was the first boy to become a pupil at the original school. He joined Bomber Command and flew an incredible 50 missions over enemy territory. He and three other old boys were all awarded the Distinguished Flying Cross.

Other notable old boys include artist Quentin Blake, famous for his illustrations of Roald Dahl's children's books, and Will Hutton, current editor of The Observer.

The school moved as a boys' grammar school into its present home in Hurst Road in 1954 to give it room to expand.

Mr Wells wrote the book at the invitation of the present head Jim Rouncefield as his "retirement project".

It has taken him all over the country, kept him poring over dusty archives and put him in touch with many former pupils, including Carreck, now in his 80s and living in Portugal.

The book is launched at the school on Friday and is available from the school finance office, priced £10 plus £2.50p&p if sent by post. Call 020 8269 9706