The Nazi leader hatched a plan to land his forces on the south coast in 1940.

They were then expected to take all the major towns and cities in their path, as far north as Northampton.

Once they had conquered the town, Hitler expected the rest of the demoralised nation would crumble and quickly succumb to German occupation.

The details of Hitler's doomed masterplan, known as Unternehmen Seelowe – which translates as Operation Sealion – are revealed in a book published this week by Oxford's Bodleian Library.

German Invasion Plans for the British Isles, 1940 is a compilation of three Nazi portfolios which have been stored deep in the library's archives for decades.

Bodleian spokeswoman Oana Romocea said: "A lot of research was carried out by the Germans in the 1930s and some of that information appeared in these documents, which were used by Hitler's generals to compile the invasion plan called Operation Sealion.

"The library has one of the few copies of the documents to survive and we want to make our archives available to the public."

The invasion plan included detailed maps and aerial photographs of major routes and tactical targets in the UK, as well as a guide to British weights and measures, money and an English and Welsh phrase book.

Had Operation Sealion not been abandoned, Hitler's forces would have had to contend with the resistance of Northamptonshire's Home Guard.

Ronald Hodnett, now 84, was serving with what was then known as the Local Defence Volunteers in Boughton in 1940, the year of the planned invasion.

But he said the lack of organisation meant the village's "Dad's Army" was severely limited in what it could have done to repel the threatened German invasion.

He said: "We were under instructions to look out for German paratroopers or enemy agents and if we saw them we were to report it.

"We didn't have any guns and even those units who had were unlikely to have had any bullets.

"The best we could have done was point the gun at the enemy and hope he would surrender."