With technical notes scrawled over it, this book of faded colour maps and postcard snaps appears to be little more than an uninspiring aerial survey of England’s coastline.

But it is actually an original war dossier of Hitler’s planned invasion of Britain. The 446-page document is now set to fetch up to £500 during a Mullocks auction sale at Ludlow Racecourse on September 30.

Unveiled for the first time 70 years after Hitler’s planned onslaught of the south coast, the blueprints offer a chilling insight into what could have been on the morning of September 15, 1940.

The book pinpoints quaint English coastal towns earmarked for destruction, which could have been a grim reality had the RAF not performed so valiantly against the Luftwaffe during the Battle of Britain.

It also shows how postcards identifying unmistakable landmarks such as Brighton Pier and Lands End, were given to Nazi troops to identify their targets in preparation for their blitz of the British Isles.

The original copy of the Nazis’ briefing book – Militargoegraphiscke Angaben uber England Sudkuste – for Operation Sealion detailed every attack point and weakness along England’s south coast ahead of the German’s assault in September 1940.

It is said to have been the most vital part of the extensive attack plan and included large colour maps showing all corners of the south coast, from Land’s End in the south west to Foreness Point in Kent.

Hitler’s forces were forced to postpone Operation Sealion after losing air supremacy over England in the Battle of Britain.

The Nazi offensive never took place but experts believe the book for Operation Sealion reveals how Britain could have ended up if beaten in the Second World War.

Richard Westwood-Brookes, from Mullocks Auctioneers, said: “The book on Operation Sealion gives a fascinating insight into what life could have been like if the Germans had invaded. It would only have been issued to a few high-profile Nazi officials in advance of the invasion, which was due to take place soon after.”

By Sophie Bignall