The prince was checking the BM's exhibition of Treasured Miniatures - Contemporary Netsuke a few hours before he formally declared it open, and I was privileged to hover in his imperial wake. Lawrence Smith, director of the BM's Japanese antiquities department, was at his side making notes; the prince gazed with exasperation at a butterfly bursting from its chrysalis which was labelled Baku - Madonna and Child: a baku, depicted further along the showcase with a baby at the breast, is a mythical Japanese beast. The captions were indeed reversed; Smith added to his copious list of notes.
The perfectly groomed, 39-year- old prince, who speaks fluent English, is Japan's leading collector of contemporary netsuke - miniature sculptures of a special type that used to be part of a gentleman's dress. Up to the late 19th century they were used with kimonos as toggles or buttons that attached pouches to the belt. Now they are simply made as showpieces. Extraordinary artistry was, and is, lavished on them; in miniature format carvers depict animals, bugs, birds and myths with detailed realism and humour.
From around 1868, when the Japanese abandoned the kimono in favour of Western dress, to around 1970, netsuke were only made as cheap tourist souvenirs, or, occasionally, as an amusing exercise of craftsmanship by carvers normally specialising in ivory sculptures. Over the past 20 years, however, new life has been breathed into the tradition and there are now around 100 professional netsuke carvers world-wide, making tiny works, often of dazzling virtuosity. The overall standard of carving is much higher than in the days when they were made for use.
Not only has netsuke carving been revived in Japan but a small, enthusiastic band of non-Japanese carvers has sprung up - in Britain, America and Australia. Michael Webb, a former director of Sotheby's furniture department, is the top exponent in Britain. He carves dazzling frogs and lizards in a Yorkshire retreat and sells them through Eskenazi's gallery in Clifford Street, London W1. Prince Takamado is the patron of the International Netsuke Carvers Association, which was founded in 1982, and the chief promoter of the art form, both at home and abroad.
He explained to me that he was introduced to netsuke by his wife, Princess Hisako, who was already a keen collector before their marriage in 1984. She is the daughter of a banker, was brought up in England and went to Cambridge University - and picked up her interest in netsuke in Europe. Ten years ago netsuke were much better known in the West than in Japan itself. According to the prince, roughly 80 per cent of Japan's redundant netsuke were exported to Europe at the end of the 19th century. Western collectors became fascinated by their sculptural qualities, while they were not valued in Japan. Since the Second World War the Americans have become the main collectors, though there are regular sales and exhibitions of old netsuke in London and Paris.
'I gave my wife a netsuke as a birthday present in 1984 just before getting married,' the prince told me. 'It was a carving of a horse, the animal representing my sign in the Oriental zodiac. I was surprised that such a small object could cost so much - the price is such that it really is not the sort of present one would ordinarily give someone.'
He's right. Contemporary netsuke are enormously expensive. Few of them measure more than 8cm (3.1in) across but average prices run from pounds 1,500 to pounds 3,500 - the very top pieces can sell for pounds 10,000 or more. Collectors who are used to buying antique netsuke, where prices first soared in the 1970s and have continued to climb, look on modern netsuke as a 'cheap' alternative - which helps maintain their price level. Japanese retailers take a very large cut; the carvers often receive as little as one-third of the sale price.
The exhibition at the British Museum, which moves on to the Los Angeles County Museum in May, is the first serious international show devoted to this curious art. All the netsuke have been carved over the past four years and all are drawn from private collections in Japan - many from that of Prince Takamado.
Despite the fact that modern netsuke are not used - except, perhaps, with ceremonial dress on a special occasion - they are expected to have the same characteristics as old netsuke. They must have no projecting elements to catch on clothing; they must have holes (himatoshi) for a cord to pass through; the composition must be fully three-dimensional - looking good from every angle - and they should fit comfortably in the palm of the hand. The ingenious adaptation of animal anatomy to fit these requirements is prized, as is the finish - every hair is carved on the back of a mole or mouse - and a touch of humour is a bonus. For instance, the exhibition includes a frog outraged to find a gold spider under his mushroom home by carver Kiho Tagaki; it is titled 'No trespassing'.
There have always been wooden netsuke but ivory has, until recently, been the carvers' and collectors' favourite material. The Washington Convention of 1989 on the protection of flora and fauna imposed a ban on international trade in ivory which was initially a blow to the netsuke carvers. It has goaded them to seek out new materials which are stunningly revealed in this show.
Kiho's frog and mushroom are carved from a South American tagua nut, with the flesh variously tinted. Bishu Saito, the president of the Carvers' Association, is showing a dancing rabbit with human breasts carved from an excavated mammoth tusk, a swan carved from amber and a stalking jaguar from guayacan wood from Ecuador - which has a marvellous, natural spotted texture.
But my favourite among Bishu's collection is called 'Boundless Love' and depicts two whales smooching in the deep. The subject was suggested to him by Prince Takamado. 'Bishu showed me this stick of fossil whale bone he'd got hold of,' the prince told me, 'and asked what I thought he should carve. I suggested he turn it back into a whale - so he did.'
The main dynamic behind this revival has come from the US. In the postwar years an American lawyer, Raymond Bushell, settled in Tokyo where he formed a huge collection of historic netsuke and wrote the books that introduced them to American collectors; he recently donated 650 to the Los Angeles County Museum. He has also supported contemporary artists, notably Masatoshi Nakamura, the oldest carver in the BM show and one of the best.
It was not until 1983 that Masayoshi Yamada, a dealer in ivory carvings and personal seals, organised the first exhibition of contemporary netsuke at a branch of the Seibu department store chain. The Seibu exhibition, now run by his widow, has become the great annual event in the field; in 1984 the show visited 24 branches of Seibu across Japan. Meanwhile Prince Takamado, seen regularly on Japanese television extolling the virtues of netsuke, has brought the collectors flocking.
'Treasured Miniatures' continues at the British Museum until 17 April