New evidence of how far Wallis Simpson was prepared to sacrifice herself to allow her lover Edward VIII to remain on the throne is revealed in the Monckton papers released yesterday.

A handwritten document signed by the future Duchess of Windsor and which might have changed the course of history says: "With the deepest personal sorrow Wallis Simpson wishes to announce that she has abandoned any intention to marry His Majesty."

Though the document was undated it is assumed to have been written at the height of the abdication crisis in December 1936. It was written in pencil in the handwriting of Lord Brownlow, one of the duchess's courtiers, when they were staying at Lou Viei, her villa in Cannes.

The document was apparently unearthed in 1948 among political papers belonging to the prime minister at the time of the abdication, Stanley Baldwin. They are referred to in correspondence between Walter Monckton, the Duke of Windsor's confidant, and Alan Lascelles, the king's private secretary.

It seems that Mrs Simpson's signed note was never seen by George VI, Edward VIII's successor, or his wife, now the Queen Mother.

Though Mrs Simpson issued a press statement at the time of the abdication referring to her wish to avoid any action that would damage the king, and was willing to "withdraw", the document released yesterday goes much further.

Its existence surprised Lascelles who asked for copies of all Monckton's material on the abdication crisis. Monckton replied: "I will see to it that the abdication material ... is delivered to you for Windsor [home of the royal archives] as soon as it is available."

The prevailing view, however, is that Edward VIII had made up his mind to relinquish the throne to marry the woman he loved. Papers released yesterday show that the future duchess's lawyer - Theodore Goddard - told Downing Street that "his client was ready to do anything to ease the situation but the other end of the wicket [Edward VIII] was determined."

The Monckton papers paint a picture of growing hostility between London and France - where the duke and duchess exiled themselves - and between the two royal brothers. They include a letter sent by the duke to Neville Chamberlain, the prime minister, in 1938 with the former king mentioning he had attached copies of his correspondence with George VI.

This correspondence - along with many other papers - is missing from the Monckton documents. However they give a flavour of the tension between the two men with the duke describing his brother as "stupid and rather impertinent".

The papers also reflect the depth of the duke's resentment at what he regarded as the unfair way in which he was treated, including the rebuff of his repeated attempts to return to Britain.

Yet on the day before the war began - September 3 1939 - when George VI offered to send his personal plane to France to fetch the duke and duchess, the former king responded by saying that unless he could use one of the royal houses they would not return to England.

The British ambassador in Paris noted that the duke had wanted two aeroplanes to take "a maid and of course luggage".

The papers contain a long personal account of the abdication crisis written by Monckton a few months afterwards. Monckton argued that the public could not understand the events of the abdication unless they appreciated two factors.

The first was the "intensity and depth of the king's devotion" to Wallis Simpson. "To him she was the perfect woman. It is a great mistake to assume that he was merely in love with her in an ordinary physical sense of the term. There was an intellectual companionship and there is no doubt that his lonely nature found in her a spiritual comradeship."

Monckton referred to the king's abdication speech on December 11 1936. "When he said in his final broadcast that he could not carry on his task without her by his side, he said what he really meant from his heart."

Monckton believed that the second factor was "much less generally recognised" by the public.

The duke had "remarkable determination, courage, and confidence in his own opinions and decisions." He added: "Once his mind was made up one felt he was like a death adder 'that stoppeth her ears and refuseth to hear the voice of the charmer'."

Monckton believed that in the quandary of his marriage or his throne, "the trouble was that ... his mind was made up for himself long before he knew it." This, Monckton believed, was "the explanation of what must have seemed to many strange and obtuse obstinacy."

Monckton wrote: "For myself I am free to confess that I always underestimated the depth and strength of the king's devotion and of their united will."

Monckton added a later note saying that the duke had told him that he had made up his mind to marry her in 1934, "and from that time onwards, his mind never wavered".

The private papers contain one letter written by the queen, now Queen Mother, to Monckton - an anodyne query in June 1941 about the official work of her brother, David Bowes-Lyons.

The papers show that 11 days after her lover abandoned the throne Wallis Simpson was upset with the model of herself in Madame Tussaud's. She complained to her lawyers: "Is there any way you can have that appalling wax figure of me removed from Madame Tussaud's - it really is too in decent and so awful to be there anyway."

But they found that there was no legal way of forcing Madame Tussaud's to remove the figure.

At the outbreak of war, the duke was given the rank of major general as liaison officer with French forces in Paris. After France was overrun in the summer of 1940, the duke and duchess fled to their villa on the Riviera. They then moved to Spain where the duke responded to flattery from Franco and German diplomats by saying how much he wanted peace. The couple subsequently moved to Portugal where the duke ignored Churchill's instructions to return to Britain. He was finally persuaded to take up a governership of the Bahamas in 1940.

The telegrams exchanged with Hitler

The papers shed no new light on the Duke of Windsor's relationship with the Nazi regime. The duke and duchess had visited Germany as Hitler's personal guest in 1937.

The papers, however, do contain copies of telegrams exchanged between the duke and Hitler shortly before the outbreak of the second world war.

On August 24 1939, the duke wrote of "my entirely personal, simple though very earnest appeal for your utmost influence towards a peaceful solution of the present problems".

Hitler replied saying it depended "upon England whether any wishes for the future development of Anglo-German relations materialises".

German documents referring to the duke and his alleged sympathies with Nazi Germany were published in the 1950s despite fierce opposition from Churchill. An introduction insisted on by the government says: "The duke was subjected to heavy pressure from many quarters to stay in Europe, where the Germans hoped that he would exert his influence against the policy of his majesty's government. His royal highness never wavered in his loyalty to the British cause or in his determination to take up his official post as governor of the Bahamas on the date agreed."

• Monarchy