Hidden treasures: From fragments of Mars to Van Gogh's sketchbook and Newton's apple tree, the secrets of the world's museums revealed

As a writer for the BBC TV show 'QI', Molly Oldfield spent hours wandering around museums soaking up inspiration for questions.

But it was while delving through the archives of the Natural History Museum that she hit upon the idea for her book 'The Secret Museum' which presents to readers spectacular treasures from around the world which are hidden from display.

The reason they are hidden from view is not because of obsessive secrecy rather the items size, fragility and value prevents them being displayed.

From the flag captured from the Spanish at the Battle of Trafalgar, to fragments of Mars rock and cuttings of the apple tree which inspired Isaac Newton's theory of gravity, all are revealed within 'The Secret Museum'.

The Vatican Observatory owns these three meteorite fragments from Mars (above). These billion years old rocks which have travelled 140million miles before reaching Earth have all had their authenticity tested using data obtained by the Mars Rover.

The original apple tree which inspired Isaac Newton to discover the theory of gravity stood in the garden of his childhood home in Lincolnshire.

In 1800 the tree was uprooted and another grew in its place but some pieces of bark from the original tree (pictured above) were saved and are now kept in the Royal Society archives, London. Oddly enough, they also have a lock of his hair.

The vast Spanish flag seized by the victorious Royal Navy after the Battle of Trafalgar is the biggest flag in the National Maritime Museum's Collection, London.

It is 10m long and 14.5m high and has never been displayed at the Museum simply because it is so fragile - and too big.

The Diamond Sutra (above) - found in China - dates from AD 868 and is the earliest dated printed book in the world.

The Sutra is a teaching given by Buddha to his disciple and is a scroll nearly 5m long. The paper is very delicate and does not react well to light.

It is now kept inside a wooden box in a special vault with other precious books in the British Library, London.

Four of Van Gogh's sketchbooks are kept in the archives of the Van Gogh Museum, Amsterdam, The Netherlands. Throughout his life he kept a book like this within reach in his pocket so he was able to react quickly to what he saw.

The first image Van Gogh sketched in this particular book was a church in Nuenen, The Netherlands (pictured above).

Jason Junior was the robot which first set eyes on the Titanic 74 years after it hit an iceberg and then sank to the bottom of the Atlantic Ocean.

Jason Junior is a blue Remotely Operated Vehicle (ROV) attached by a cord which transmits data and was sent to the ocean floor to explore the wreck. It is now housed in the archives of the MIT Museum, which is full of remarkable robots and machines, in Massachusetts, U.S.

• 'Secret Museum' by Molly Oldfield is available from Amazon priced £17.