The nationalisation of Fannie Mae and Freddie Mac, and the bankruptcy of Lehman Brothers take us into the most dangerous financial territory since the 1930s. Of course there are similarities to earlier crises. The attempts by Fannie and Freddie to trade their way out of problems on an outrageously thin capital base are redolent of the savings and loan fiasco of the 1980s. As in the mid-1970s and the early 1990s, property has been at the heart of the maelstrom, with bankers and regulators in the US pinning their colours to the fabulous notion that national house prices never fall.

The financial markets' categorical imperatives - greed and fear - played their part in creating what proved to be the biggest credit and housing market bubbles in history. But this time some things are genuinely different.