The young air attaché at the British Legation in wartime Sofia was more than a little surprised to have his weekend disrupted by ‘a beautiful young Polish woman’ and a ‘round-faced, jolly ex-Polish officer’. The pair claimed to have driven from Budapest with urgent military intelligence. It was still early on the last Sunday in February 1941, but, as across Eastern Europe, the atmosphere in the beautiful Bulgarian capital was tense. After a quick glance at his ‘two unusual visitors’ and their dilapidated Opel Olympia, abandoned in the street, the attaché, Aiden Crawley, ushered them inside. As soon as the door closed, Krystyna Skarbek handed over a letter of introduction from the British Ambassador in Budapest, and a roll of ‘Foto-Plat’ microfilm, which she had concealed inside her gloves.

Although a Polish national by birth, Skarbek was the first woman to serve Britain as a special agent during the Second World War, and the film footage that she had risked her life to deliver was of the highest military significance. Filmed by members of an independent Polish resistance group, it showed the massing of hundreds of tanks and troops on what was then the German side of the Nazi-Soviet wartime border. There were also photographs documenting the creation of a series of fuel and ammunition dumps, clearly in support of a mechanised invasion. ‘This was the first positive evidence’, Crawley later wrote, that Hitler was making large-scale preparations for an aggressive campaign against his erstwhile Soviet ally. Should the Führer now make an enemy of Stalin, he knew there was potential for a British alliance with a world power whose military and economic resources might well prove decisive for the outcome of the war.

Even as Skarbek and her companion, Andrzej Kowerski, a veteran of the September 1939 Polish campaign, were being thoroughly debriefed, Crawley was forwarding the microfilm to the British Air Ministry, who sent it straight to Churchill.

‘That Germany should at this stage, before clearing the Balkan scene, open another major war with Russia seemed too good to be true,’ Churchill noted cautiously. It was only after the veracity of the microfilm footage was supported by reports on extensive troop movements towards the Soviet border from ‘Ultra’ – the German intelligence signals being decoded at Bletchley Park – that the prime minister considered issuing a warning to Stalin. By then, Skarbek and Kowerski were back on the road. They travelled through Turkey – where they narrowly escaped the bombing of their hotel – Vichy Syria; Lebanon, which was then also in the French Mandate; and Palestine, before reaching the safety of the British base in Cairo. Yet, to their disgust and rage, on arrival they found themselves denounced as suspected double agents and officially put on ice.

Some of the concern was the apparent ease with which the two had travelled through hostile territory, but the British knew that visas could still be obtained at a price. More of an issue was the politics of British Egypt. ‘Nobody who did not experience it can possibly imagine the atmosphere of jealousy, suspicion and intrigue which embittered the relations between the various secret and semi-secret departments in Cairo’, the regional director of the Special Operations Executive (SOE) later wrote. Skarbek had arrived at the height of the ‘spy mania’, during which her Polish resistance contacts had fallen from favour. Despite Churchill’s direct warning to Moscow, it was June before one of the greatest invasion forces in history tore through Stalin’s ill-prepared border defences and ploughed relentlessly on towards Stalingrad. Operation Barbarossa would turn out to be a terrible miscalculation by Hitler, forcing his erstwhile collaborator, the Soviet Union, to join the Allies. Incidentally, it vindicated Skarbek and Kowerski, who were now transferred into SOE to resume active duties.

The first record of Skarbek in the British files is a Secret Service memo dating from December 1939, which records her as a ‘flaming Polish patriot… expert skier and great adventuress’. Demanding to be taken on rather than merely volunteering her services, she had submitted a bold plan to ski into Nazi-occupied Poland from Hungary, via the Carpathian mountains, to gather intelligence for the Allies.

Skarbek had been with her second husband, a diplomat posted to southern Africa, when Nazi Germany invaded Poland, plunging the world back into war. By the time she reached Britain on a passenger ship, travelling in slow convoy, her homeland had been occupied and the Polish government and 35,000 troops had evacuated to regroup in France and continue the fight. The way Skarbek saw it, the fastest way to serve her country was to smuggle British money, information, and propaganda into Warsaw to bolster the Polish resistance at a time when many Poles believed they had been abandoned to their fate. She could then return with vital intelligence from within the first nation to be occupied.

Skarbek spoke the right languages, had extensive contacts, and even knew the smuggling routes across Poland’s mountain border passes, because, as a bored countess some years earlier, she had smuggled cigarettes, simply for the thrill of it. ‘She is absolutely fearless,’ MI6 closed their report. Signing her up despite the then problematic twin issues of her foreign nationality and female gender, she was given a false identity as a French journalist, some basic training, and a selection of trusted contacts in Budapest. She was in place and planning her first clandestine trip to Poland before the year was out.

It was February 1940 when Skarbek had first skied over the freezing Tatra mountains and into enemy-occupied territory. ‘The wind swept like a sword across forest, plain and mountain’, a fellow British agent later wrote melodramatically. ‘Birds in the trees were frozen to the branches… and there was blood on the snow to mark the passage of starving wolf-packs.’ Skarbek had encountered neither frozen birds nor starving wolves, but she did pass the corpses of a young couple who had frozen to death in the mountains as they tried to flee the Nazi advance. Eventually, Skarbek crossed into Poland, hid her skis, and caught a train to Warsaw. There, she established contact with the fledgling Polish resistance, then travelled the country by train, hitching lifts in trucks and carts, noting troop numbers, the requisitioning of Polish property and industry, and her compatriots’ morale. Within a few weeks she had returned to Budapest with her own first-hand intelligence, as well as radio codes and coding-books to enable direct British communication with the resistance.

One year later, Skarbek set out on her fourth mission into Poland. Her objectives were to help with the evacuation of some downed pilots hiding in a hospital, and to collect a very specific microfilm. After a close shave with German patrols in the mountain forests, she was forced to return empty handed, only to be arrested hours later at the apartment of her lover, Andrzej Kowerski. Despite being badly beaten during his interrogation, Kowerski stuck to his cover story. It was Skarbek, however, despite now being feverish with the flu, who secured their release.

Making a virtue of her apparent weakness – her temperature and hacking cough – Skarbek bit her own tongue hard and repeatedly. She now appeared to be coughing up blood, the well-known symptom of TB. Rightly terrified of this infectious disease, and after a brief examination by the prison’s Polish doctor seemed to confirm the diagnosis, Skarbek was released. It was a ruse that SOE would later include in one of their handbooks for agents.

Rightly presuming that Kowerski was Skarbek’s lover, and so likely to be infected, the German prison officers threw him out as well, although the pair were followed from a safe distance. With the help of some trusted resistance contacts, the British Ambassador in Budapest, new false papers and a stolen car, Skarbek and Kowerski managed to lose their tail and cross into Serbia. It was in Belgrade, possibly in the belly-dancing bar where the ambassador had arranged to rendezvous with them, that Skarbek had collected the precious Polish microfilm. As soon as this was safely stowed in her gloves, she and Andrzej had driven on to deliver it to Crawley in Bulgaria.

In Eastern Europe, Skarbek had gathered and delivered high-grade intelligence and, once her name had been cleared, she served in another intelligence role in Egypt. She also undertook operational missions in the region, and was trained in Morse, wireless transmitting, the use of weapons and explosives and – a course she excelled in – silent killing. In the summer of 1944, she would serve in a third theatre of the war. That July she became the only woman to parachute from North Africa into German-occupied southern France in preparation for ‘D-Day in the south’: Operation Dragoon. She was to be the courier for SOE’s ‘Jockey’ circuit, established and run by Francis Cammaerts, by whose side she quickly saw action during the ill-fated Battle of Vercors, a premature uprising of the Maquis. Skarbek was most effective, however, when she operated alone.

Discovering that the German garrison on the strategic Col-de-Larche pass in the Alps was partly manned by Polish conscripts, in mid-July Skarbek scrambled up the goat tracks through the trees until she reached the concrete, stone and strengthened steel platform at the edge of the garrison fort. Armed only with a white and red headscarf, the colours of Poland, and a discrete loudhailer, she called out to a pair of Polish perimeter guards in their native tongue. A frantic conversation ensued, during which she won the men’s trust. A week later Skarbek returned, persuading the more than 60 Polish conscripts at the garrison to defect on a set date, but not before rendering their heavy-weapons useless by removing their breech-clock firing pins, and collecting as many mortars and machine-guns as they could to bring down to the French resistance. It was through Skarbek’s ‘own personal efforts’ that she achieved ‘the complete surrender of the Larche garrison’, Cammaerts later wrote. While in his citation for her, the local general reported that her work ‘had not been short of remarkable’ and ‘of the greatest value to the Allied cause’.

Skarbek is perhaps now best known for her last single-handed operation in France. Returning from the Col-de-Larche garrison, she discovered that Cammaerts and two other Allied officers had been arrested and were scheduled for execution the following evening. Having cycled 20 miles cross-country to the prison where they were being held, she marched in, demanded to see the senior officer, and declared herself a British agent – evidenced by a broken wireless crystal. Having added for good measure that she was General Montgomery’s niece, she went on to terrify the prison governor with tales of the rapid American advance, offering to either speak for him if he released the men, or to see him strung up from the nearest lamppost. It was only when she was driving off with Cammaerts and his colleagues that it became clear how far away the American lines still were.

Skarbek survived the Second World War, adopting the name Christine Granville, one of her nom-de-guerres, to take British citizenship in 1946. She was honoured for her service with the George Medal and OBE, as well as the French Croix-de-Guerre. Not only the first woman, she was also Britain’s longest-serving special agent, male or female, and among the most effective. Yet she died young, murdered by an obsessed stalker in London in 1952. Several books and a proposed film of her life were shelved and, despite rumours that she was the inspiration behind Ian Fleming’s first femme fatale, Vesper Lynd, Skarbek’s story was slowly forgotten. At least by most. The actress Sarah Oliver, Winston Churchill’s second daughter, who had been cast in the lead role for the abandoned biopic, told a reporter that ever since the Operation Barbarossa microfilm had arrived in London, Krystyna Skarbek had been the British PM’s ‘favourite spy’.