‘Japanese men are literally mother…ers!’ This exuberantly expressed opinion was given by a fellow gaijin (foreigner) when I was living in Tokyo. He had learned from a Samaritan that motherly guilt for having sex with their sons was Japan’s main psychological problem.

I had been seeking confirmation after a conversation with a young Japanese psychoanalyst; ‘What is the most common problem you have to deal with?’ I asked. ‘Incest’, she replied instantly,’ Japanese boys often have their first experience of sex with their mothers.’ In a world in which incest is normally between fathers and daughters, this revelation came as a surprise. How had I missed this?

In fact, the secret was hiding in plain sight. While not openly discussed, the dominant-mother complex is a recurring theme of Japanese literature. Suddenly Japan’s incest problem made sense of Abe Kobo’s most famous novel, The Women in the Dunes, which won the Yomuiri prize (the equivalent of the Georg Büchner Prize) in 1960. The subject is even more explicitly explored in Fumio Niwa’s story, The Buddha Tree, where the main character is adopted and then seduced by his foster-mother.

What are the sociological reasons for the peculiarities of Japan’s mother-son relationships? The roots of Japan's matriarchal society run deep. Unlike Christianity in which God is portrayed as a man, in Japan God is a woman. In Shinto tradition, Japan's current Emperor, Naruhito, is descended from the sun goddess, Amaterasu Omikami. Women dominated both literature and the court in the early Japanese history and ruling empresses were common until the 8th century.

More prosaically, women traditionally return home to their mothers for the birth of their first child. From that point onward wives often sleep more with their all-important sons than with their husbands. Boys may still be sleeping with their mothers late into their pubescent teens. This does not suggest that these relationships always lead to penetrative sex, though some clearly do.

In later life this leads to peculiarities in male behaviour. As Edwin Reischauer, the erudite former United States ambassador to Japan wrote: ‘A husband sometimes seems to be the wife’s big grown-up child, requiring tender care and pampering like the other children, or else he shows the need for special feminine attention and flattery from other women . . . as from geisha in earlier times or bar girls today.’ Indeed, in the 1980s Tokyo's Shinjuku area sprouted ‘mummies’ clubs’ where tired businessmen could act out erotic fantasies with ‘surrogate mothers.’

This brings us to the most critical functions that Japanese mothers perform for their sons — marriage and education; the success of the former being largely dependent on academic and career advancement. This perhaps is the crux of the mother-son relationship. By western standards remarkable sacrifices are made for the attainment of academic qualifications. Boys are forced to attend juku (cramming schools) that supplement the already onerous state education system. It is estimated that by the age of 12 the typical Japanese boy may have received as much as four years' tuition more than his western counterpart.

The mother-son complex that pervades Japanese society is contrary to the mythology that developed in the west in the 19th Century that Japan is a male dominated society. Western culture is embedded with this shibboleth from works such as Puccini’s Madama Butterfly (1904) to the James Bond movie You Only Live Twice (1967).

My first experiences of Japanese life might well have supported the traditional view of a male-dominated Japanese society. When I first went to live in Japan I stayed for three months with a Japanese family near Ofuna. I would frequently return late at night after hours of heavy drinking with Japanese businessmen in Ginza bars to find my host’s wife waiting up for me on the step inside the front door of her house.

Hearing the crunch of my step on the gravel outside, she, dressed in a kimono, would jump up, and bow deeply. She would then rush to pour my bath, fix me something to eat and roll out my futon. No matter what time I returned at night, she would be up at 5 o’clock the next morning to prepare my breakfast so that I could catch a 6 am train for my 90-minute commute into Tokyo.

However, despite her hospitality, I never felt like the dominant sex in this relationship. Quite the opposite. The household was her domain; she served but controlled. Her husband, a middle-ranking executive at Toshiba, was a meek and minor player in the household drama - a worker bee for his queen. Early on I resolved never to contemplate marriage to a Japanese woman.

An expat banking friend, underwhelmed by the level of productivity in his department, decreed a ban on all overtime pay and ordered his employees to leave the office by 5.30 pm. A delegation soon appeared at his door pleading to be allowed to stay later. The men would lose face if they returned home early as their wives would suspect that their careers were going nowhere and would punish them accordingly.

The traditional view that Japanese executives leave their wives to wither at home while they go off to the eating shops of Shimbashi or the drinking dens of Ginza, is entirely wrong in attributing their behaviour to a male-dominated society. The reason they do not go home is that they are often not wanted by their wives, who disparagingly refer to their husbands as gokiburi (cockroaches). Even the famed Japanese 'love hotels', the gothic concoctions, sometimes fantasy castles or ocean liners, supposedly used by Japanese businessmen for illicit liaisons, are frequently used by henpecked husbands just to watch their favourite television programmes.

The most laughable case of Japan's bolstering of its masculine image occurred in the early 1980s, when the prime minister, Yasuhiro Nakasone, explained that Aids was only a western disease…because there were no Japanese homosexuals. Yet from mediaeval times homosexuality was quite openly practised among samurai warriors and within the Buddhist priesthood. More recently, Japan's best-known post-war novelist, Yukio Mishima, acquired his fame through homoerotic novels such as Confessions of a Mask and Forbidden Colours, which would have been unpublishable in many European countries in the 1950s. Meanwhile, the gay quarter of Shinjuku is hardly Tokyo's best kept secret.

Today Japan remains the only G7 country where same-sex marriage is illegal despite courts which have ruled that the ban is unconstitutional. Prime Minister Fumio Kishida is under pressure from public opinion to introduce laws to give legal protection to same sex unions but has so far been unable to bring the right wing of his party into line. Polls show that 70% of Japanese support gay marriage.

But this is hardly Japan’s major sociological problem. In 1950 Japan had 27 births per thousand people; today it has just seven. On current trends, Japan’s population, having peaked at 128m in 2010 is expected to fall to 106m by 2050 and 75m by the end of the century. Clearly neither gay nor mother-son sex are Japan’s main problem. No sex seems to be the bigger issue. According to government research some 40% of people between the ages of 18 and 34 have never had sex. This is a problem on a scale which, in relation to demographics, far outweighs Japan’s other sex related issues.