T his weekend is the 80th anniversary of one of the most controversial events in British history – Prime Minister Neville Chamberlain’s notorious Munich Agreement with Adolf Hitler – and yet vast numbers of documents exclusively from that period have still not seen the light of day.

The Independent understands that around 1,750 British intelligence reports, from a four-month period immediately before the Munich Agreement and from the three months immediately after it, are missing from the record.

Significantly, they are the only intelligence files of their sort missing from the entire pre-war (1919-1939) and wartime (1939-1945) period.

Up till now, historians specialising in the run-up to the Second World War, have not known why or when they went missing. But previously unpublished information given by one of the government’s key intelligence organisations, GCHQ, to The Independent now reveals that the material was definitely in GCHQ until 1968 – and then appears, for reasons unknown, to have been lent to another government department and never returned.

One possibility is that they were lent to help with some sort of research project undertaken by government historians to commemorate the 1968 30th anniversary of the Munich Agreement. The notorious deal with Hitler (in which Britain, France and Italy agreed that Nazi Germany could take over the majority German-speaking part of Czechoslovakia) had been the work of a Conservative-dominated administration and had been opposed by the Labour opposition – so such research would certainly, in 1968, not have displeased the then Labour government of Harold Wilson.

The revelation that the missing Munich period files were lent by GCHQ to another government department raises the distinct possibility that they still survive, buried unrecognised and undetected in a government archive. The most likely potential locations for them would therefore probably be the Foreign Office or the Ministry of Defence.

The vanished files consisted of decrypts of intercepted diplomatic communications made by GCHQ – known in the interwar years and during the Second World War as the “Government Code and Cypher School” (GC&CS).

Apart from the 1,750 missing intercept documents, all the GC&CS files were stored at GCHQ until they were transferred to the Public Record Office (one of the predecessor organisations of the National Archives) in 1999.

The new revelation, suggesting that they were lent to another government department in 1968, appears to substantially reduce the chances that the documents were removed for more political reasons, potentially to permanently bury specific information connected to the Munich Agreement itself or its aftermath.

GCHQ considers such speculation to be “outlandish”.

The organisation’s departmental historian, Tony Comer told The Independent that he considers it “likely that the 1,750 missing intercepted diplomatic messages still survive somewhere in a government department”.

If they do, they are probably still bound together between out-of-date naval charts used as makeshift hard backing for the volumes.

“The missing documents, if found, could well shed new light on precisely what Chamberlain would have known of the development of French, German and Italian intentions in the run-up to the Munich agreement,” said Mr Comer.

“The reports were those used by Britain at the time to assess what all the other governments were planning and how their policies were developing.”

The seven months covered by the diplomatic intercepts are historically extremely important because they saw many of the key developments leading up to Munich and on the road to the Second World War.

A Day That Shook The World: Hitler elected German Chancellor Show all 3 1 /3 A Day That Shook The World: Hitler elected German Chancellor A Day That Shook The World: Hitler elected German Chancellor 30th January 1933: Soldier and statesman President Paul von Beneckendorff und von Hindenburg (1847 - 1934) handing over the rule of Germany to the Nazi leader Adolf Hitler (1889 - 1945). Getty Images A Day That Shook The World: Hitler elected German Chancellor Chancellor Adolf Hitler (1889 - 1945) and Vice Chancellor Franz von Papen (1879 - 1969, centre) on their way to open the first session of the German Reichstag under Nazi rule, 1933. Getty Images A Day That Shook The World: Hitler elected German Chancellor Adolf Hitler (1889 - 1945) and Dr Robert Ley (1890 - 1945) meet a line of workers at a party congress, 1935. Getty Images

On 7 June 1938, Hitler issued his secret order to invade Czechoslovakia by the end of September. Publicly, Hitler had made it clear that he wanted Czechoslovakia to allow its German-majority districts (known in German as the Sudetenland) to be transferred to German sovereignty.

On 20 July, France secretly told the Czechoslovak government that (despite a Franco-Czech treaty) it would not help Czechoslovakia if Germany invaded.

On 3 August, a British delegation arrived in Czechoslovakia to put pressure on the Czech government to reach agreement with Germany.

The next day, German anti-Nazi generals started plotting to overthrow Hitler – and subsequently sent agents to put a secret plan to the UK government which the UK, equally secretly, rejected. Later that month, Germany sent 750,000 troops to the Czechoslovak border.

On 15 September, Chamberlain flew to Germany to meet Hitler. The following day the French prime minister flew to London. On 17 September, Germany started unofficial military activities inside Czechoslovakia.

On 18 September, Italy backed Germany over the Czechoslovakia crisis.

On 22 September, Chamberlain flew again to Germany. Hitler indicated that he now not only wanted the Sudetenland, but also wished to see the dissolution of Czechoslovakia as a country.

The next day, Czechoslovakia fully mobilised its army.

On 28 September, Britain asked Italy to join the negotiations with Adolf Hitler.

The following day, the French and British prime ministers met Adolf Hitler and Mussolini in Munich and agreed that Germany could take over the Sudetenland

On 30 September, Czechoslovakia reluctantly agreed (despite the fact that it meant losing most of its industrial areas and virtually all its major defensive installations). On the same day, at Chamberlain’s request, Adolf Hitler agreed to sign a peace treaty with Britain. Chamberlain then flew back to London – and famously announced that he had secured “peace for our time”.

As soon as Hitler’s victory in the crisis became known, the Soviets felt betrayed by France (they both had a defence treaty with Czechoslovakia). The West’s betrayal of the Czechs persuaded Stalin not to trust the West if it came to any showdown between the USSR and Germany. This was a factor which led to Stalin wanting to develop his own rapprochement with Germany (which eventually led to their infamous pact and the partition of Poland the following year).

Then in early October, Germany took over the Sudetenland. The next month, Germany and Italy forced Czechoslovakia to cede territory to Hungary. Poland then also seized part of Czechoslovakia.

In March 1939 Germany invaded the remaining parts of Czechoslovakia and took them over.