Exactly 50 years ago, cosmonaut Yuri Gagarin became the first man in space. His journey to the heavens was a pinnacle of human achievement – and, argues Rupert Cornwell, the defining triumph of the Soviet Union

Not everyone can ask the Queen what fork to use at a banquet or – as one account has it – surreptitiously squeeze her knee to make sure one is indeed a guest at the top table. But then again, not everyone is Yuri Alekseyevich Gagarin, the most perfect specimen imaginable of Homo Sovieticus who, a summer's day 50 years ago, found himself at Buckingham Palace, feted as the most famous man in the world.

Seen from this age of al-Qa'ida and the internet, the lumbering confrontation known as the Cold War is almost as distant as antiquity. Did we really get so worked up about those spy scandals, so quaint in the telling now? Did we really believe that the Russians were out to conquer us; that the East-West conflict might bring about nuclear obliteration? But indeed we did. And that is one reason why even today, Yuri Gagarin is so remarkable a figure.

By contemporary standards, what he achieved on 12 April 1961 is small beer.

His space craft Vostok I (or East I) made just a single orbit of the Earth lasting 108 minutes, 200 miles up. The vehicle was so basic that it has been likened to a tin can placed on top of a bomb.

As was their wont, the Soviets gave some false information about the flight, which was only announced after its completion. Vostok I, they said, had landed safely with Gagarin aboard. In fact, he ejected from the module and made the last 23,000ft of his journey back to Earth by parachute.

The first people to set eyes on him were not trained recovery specialists, but a peasant woman and her grand-daughter, working in the fields near the river Volga, 450 miles south-east of Moscow. The pair were terrified by this apparition from the heavens – not unreasonably, given that U-2 pilot Francis Gary Powers had been shot down over the Soviet Union less than 12 months before. Only when the intruder in a space suit assured them he was one of their own, not a dark messenger of US imperialism, were they re-assured.

But in that tin can (or, more exactly, a spherical module with a diameter of 2.3m or seven feet) Gagarin had done what no man man had done before. He had become the first human being to enter space. And for a while he redrew the very contours of the Cold War, as well. If there was ever a time when the Soviet Union seemed a somewhat less-than-evil empire, it was during the months around Gagarin's flight. The Khrushchev thaw, that in some respects prefigured Mikhail Gorbachev's perestroika, was in full swing. Yes, a charismatic young president had just taken office in Washington, but just four days after Gagarin's feat, JFK launched the disastrous Bay of Pigs operation against Cuba, proving that aggression and bullying were not Moscow's exclusive preserve.

And then there was Gagarin himself. If anyone could sell the virtues of communism to a sceptical world, he could.

Gagarin's was the last and greatest of a series of Soviet space triumphs, starting with the launch of the first satellite Sputnik in 1957. Two years later, Soviet spacecraft had made the first hard landing on the Moon and took the first photos of its hitherto unknown dark side. But with Gagarin, a stunning technological breakthrough had a human face. Russia now had its own Magellan, Wright brother or Lindbergh. But he travelled where even these pioneers had not: beyond the confines of the planet. And by common consent, it couldn't have happened to a nicer guy.

"A delightful fellow," was the verdict of Harold MacMillan, after meeting Gagarin the day before the luncheon at the Palace.

From the moment the pilot entered the Soviet space programme in early 1960, it is clear that those most directly involved with his career felt the same. He was quick, shrewd and intelligent and never frightened of responsibility. Polite but firm, he had a rare knack of pleasing his superiors without alienating his peers. He also had a sense of humour. As the field of candidates was whittled down, from the 20 initially selected to six, then two, and finally to the one chosen for the flight, everyone seemed to accept that it would be Gagarin.

On reason, it must be said, was because he was short. We imagine our heroes tall and strapping. At only 5ft 2in tall, Gagarin was almost exactly the height of chairman Nikita Khrushchev (as may be seen from film of the two bear-hugging when they met at Moscow airport).

Perhaps most importantly, Gagarin was brave. He handled pressure with an ease approaching grace. Later, he himself would recount how the doctors who monitored him were "amazed by my coolness and calmness, the stability of my psyche and the strength of my nerves".

In those days it took a brave man indeed to contemplate going into space. The training was brutal, prospective astronauts were subjected to centrifuges, extreme heat and isolation. No-one knew how a human would react to weightlessness: would he be paralysed? Would he go mad?

For that reason, Gagarin himself did next-to-nothing during the flight, which was entirely automatic and controlled from the ground: the scientists simply had no idea whether a pilot could function at all.

Only just before blast-off was he given the three-digit code (it was 1-2-5) to unlock the craft's controls in case of emergency. Gagarin being Gagarin, though, he had already wheedled the number out of one of his instructors.

The whole thing was incredibly dangerous. Many missions failed. Less than six months before Gagarin's flight, a giant R-16 rocket exploded at the test site of Tyura Tam on the Khazakh steppe. Some 120 people died, including Marshal Mitrofan Nedelin, then head of Soviet Rocket Forces – who, like Gagarin, is buried in the Kremlin Wall, final resting place of the greatest Soviet heroes. The odds were 50/50 at best that Gagarin's flight would be successful.

But he was completely unfazed. On the night before the flight Gagarin slept like a baby. When he was woken at 5.30am his pulse rate was reportedly a relaxed 64. As he prepared to board the ship, he saw his mentor Sergei Korolev, the engineer-designer; the true father of the Soviet space programme, who had clearly had a terrible night. "Don't worry, Sergei Pavlovich," he told the chief designer, "everything will be fine." Korolev loved Gagarin like a son, but was astounded nonetheless: the man who was risking his life was acting as comforter of others as well. "Poyekhali," the cosmonaut said, "let's go."

In the event, it all went smoothly. The spacecraft entered orbit and the booster-rocket separated as scheduled. "There was a good view of the Earth, which had a very distinct and pretty blue halo," Gagarin noted laconically in his official report on the flight three days later. Nor was weightlessness a great problem – "to some extent unusual, but I soon adapted myself", he wrote. Throughout, he was in communication with Flight Control by radio phone.

As soon as he landed safely, Khrushchev was informed. The Soviet leader was exultant. He couldn't resist using the flight as proof of Marxist atheism: "Gagarin flew into space but didn't see any god there."

Most of all, it was proof for Khrushchev that his country had arrived; definitive refutation of the "arrogant theoreticians" who sneered at "once-illiterate, barbaric Russia". And that, in varying degrees, was how the World felt.

America, in particular, was shocked at how, after Sputnik, its superpower rival had once again left it second-best. One Congressman even demanded the US go to a war footing – if the Russian enemy could do that, what else could he do?

Three weeks later, on 5 May 1961, Alan Shepard became the first American in space. But there was no hiding the fact that the first Mercury mission was a shadow of Gagarin's feat; a suborbital flight that merely followed a ballistic missile's trajectory, travelling 300 miles and lasting 15 minutes. Only 10 months later did John Glenn orbit the Earth. By then a chastened Kennedy had vowed to put a man on the Moon by the end of the decade – and, even more important, put America back on top.

For the time being, though, it was the Soviet Union's hour and in Gagarin they had an unmatchable advertisement for the system. No semi-senile apparatchik or sinister agent provocateur he.

Gagarin was young, vigorous and handsome; a peasant's son who had made good; a genuine working class hero who was virtually impossible to dislike. Just as he charmed Macmillan, he charmed everyone else he met as he visited other countries, most notably Britain, where he made a trip to Manchester that is fondly remembered to this day. For obvious reasons he was not invited to America. Never again would the Soviet Union's global reputation stand as high. Gagarin's successful flight and the Bay of Pigs debacle had made Khrushchev over-confident. The June 1961 summit with Kennedy in Vienna convinced him he had the untried young president's measure. Two months later the Berlin Wall went up and the following year Khrushchev disastrously over-reached himself, provoking the Cuban missile crisis, in which Kennedy called his bluff and which set in motion the internal revolt that would lead to the Kremlin leader's downfall.

The Soviet Union had reverted to type. Hopes of deeper reform faded and in October 1964 Khrushchev was toppled in a palace coup, ushering in what Gorbachev would later call a "time of stagnation". By then Gagarin was a deputy to the Supreme Soviet, confined mainly to safe desk work – he was a hero the country could not afford to lose.

Eventually, though, he was permitted to fly again as a fighter pilot and was killed during a training flight on 27 March 1968, when his MiG-15 crashed in circumstances to this day never fully explained. Once again authorities threw a veil of secrecy over the event. Almost certainly the crash was an accident caused by bad weather, a mistake by an air traffic controller or evasive action to avoid another aircraft.

But in the absence of fact, the rumours flew. Gagarin was drunk, some said. Others speculated he had become a critic of the regime, which had got rid of him.

Five months after his death, the Soviet Union invaded Czechoslovakia to suppress the Prague Spring – and banished any remaining illusion, kindled largely by Gagarin, that communism couldre-invigorate itself from within.

The miracle of humans in space that he pioneered has lost its sparkle, as well. Space travel has become mundane and repetitive; only when disaster strikes does it make headlines. True, the International Space Station (ISS) still goes about its business, in partial fulfilment of the vision Gagarin spoke of at the Metro Vickers factory in Manchester 50 years ago,"when a Soviet spaceship landing on the Moon will disembark a party of scientists, who will join British and American scientists working in observatories in the spirit of peaceful co-operation".

But forget the Moon. Between 1969 and 1972, 12 Americans walked on its surface, as President Kennedy's challenge was met.

When – indeed, if – another human will do so is anyone's guess. Last year, for budgetary reasons, President Obama killed off his predecessor's plan for a permanent, manned base on the Moon, to serve as launch pad for human missions to Mars and beyond. 28 June 2011 sees the very last launch of the US shuttle, leaving Russia's single-use Soyuz craft as the only means of getting to the ISS. The ideological rivalry of the Cold War has given way to financial calculation. Why go on with the costly and aged shuttle programme, US government bean-counters argue, when Soyuz can take NASA's astronauts to the station, at only $63m (£38.4m) per ride?

But even the Russian manned space programme is marking time.

These days unmanned robotic missions are visiting the planets of the solar system. Their pictures are breathtaking and the scientific boons they confer are doubtless considerable. But the drama of the Gagarin era is gone. Alas, peaceful co-operation is less stimulating than pioneering competition, when a pilot lieutenant from behind the Iron Curtain caught the imagination of the entire world. Such is human nature.