Among the amateur diplomats I researched for my book, Coffee with Hitler: The Story of the Amateur Spies Who Tried to Civilize the Nazis, one Liberal politician and journalist emerged as an almost forgotten hero.

Philip Kerr, the Marquess of Lothian, had first visited Hitler in January of 1935, returning home convinced of the German leader’s peaceable intentions and urging the British government to make concessions to his regime. Soon after, having admitted his misjudgment of the National Socialists (later shortened to “Nazis”), he was appointed as Britain’s ambassador to Washington, to the irritation of the Foreign Office mandarins who distrusted him as an appeaser and an amateur.

Arriving in the U.S. just days before Hitler’s army swept into Poland, Lord Lothian presented his credentials to a sympathetic President Roosevelt. He acknowledged he was hidebound by the U.S. Neutrality Acts and the isolationist influences over the upcoming presidential election, and so suggested the Allies needed to convince the American public directly that they deserved U.S. support against Germany.

Dressed in a crumpled suit rather than the customary diplomat’s uniform of gold lace, the new ambassador had emerged smiling from the White House on August 30, 1939, to chat with the waiting newspapermen when a small black kitten (quickly nicknamed “Crisis”) appeared at his feet. Lothian deftly scooped up the feline onto his shoulders, creating a photo opportunity that was syndicated in newspapers across the country.

Lothian, right, with the French ambassador to the U.S. René de Saint-Quentin, leaving the White House after a conference with President Roosevelt, 1940.

Lothian served for just 16 arduous months, during which he toured 44 states, giving speeches highlighting the Nazi threat to world order. His first breakthrough was the transfer of American destroyers to the Royal Navy in exchange for U.S. naval and air bases being located in British Dominions, soon followed by the repeal of the embargo on the sale of munitions to the Allies.

But, by the winter of 1940, Britain’s finances were parlous. Arriving in New York following a meeting with Winston Churchill (and seriously ill through overwork), the British ambassador was met by journalists at the dockside. Ignoring diplomatic niceties, Lothian admitted, “Well boys, Britain’s broke; it’s your money we want.”

Just weeks later, Lothian died unexpectedly of blood poisoning, aged 58, provoking an outpouring of admiration on both sides of the Atlantic. Churchill eulogized him as “our greatest ambassador to the United States” to Roosevelt, who cabled his shock to the King. The U.S. government honored Lothian with a state funeral, arranging a cavalry escort as his coffin, draped in a Union Flag, was drawn by horses on a gun carriage to Arlington National Cemetery.

Though he lived to see neither signed, Lothian’s charm offensive laid the foundations for both the Lend-Lease Act, allowing the supply of military hardware, food, and clothing under generous payment terms to the Allies, and the Atlantic Charter. The latter, signed in August 1941, set out the principles for the establishment of NATO and the dismantling of the British Empire.

Despite this pivotal influence, Lothian remains an obscure figure and still divides his audience. Specialist historians of Anglo-American relations acknowledge his sophisticated diplomacy, while critics of appeasement paint a picture of a gullible amateur duped by Hitler. Surely he deserves better.

Charles Spicer’s Coffee with Hitler: The Story of the Amateur Spies Who Tried to Civilize the Nazis will be published on September 6 by Pegasus