The FTSE 100 plunged today, with banks responsible for much of the decline as they look set to get hit by a double-whammy from debt rating agency Moody's and the US Federal Housing Finance Agency. Shares in banks fell back after a report said that the ratings agency Moody's is set to lower its ratings on Lloyds, RBS and other British banks. Meanwhile, the Federal Housing Finance Agency signalled its intent to sue 17 banks which it claimed mis-sold it mortgage backed securities, in a move which could spark copy-cat legal cases.Randgold Resources offered the only ray of sunshine with a rise of less than 1% after the price of gold closed in at $1,900 an ounce.FTSE 100 - RisersRandgold Resources Ltd. (RRS) 6,710.00p +0.60%FTSE 100 - FallersRoyal Bank of Scotland Group (RBS) 21.94p -11.67%Lloyds Banking Group (LLOY) 30.57p -7.68%Barclays (BARC) 153.45p -7.11%Legal & General Group (LGEN) 94.20p -6.64%Xstrata (XTA) 955.00p -6.23%Aviva (AV.) 305.30p -6.09%Johnson Matthey (JMAT) 1,555.00p -6.04%Eurasian Natural Resources Corp. (ENRC) 620.50p -5.77%IMI (IMI) 804.00p -5.74%Prudential (PRU) 563.00p -5.70%NR