The Japanese government received a humiliating blow yesterday when Moody's, the US credit-rating agency, downgraded Japan's domestic currency debt for the second time in two years. The downgrade leaves Japan's yen-denominated debt rated at Aa2 by Moody's, two notches below the top-rated Aaa level - one of the lowest ratings for any large industrialised country. Moody's hinted that it might cut this further.