The Bank of England produce a very nice aggregate measure of liquidity conditions. It is a simple unweighted average of nine liquidity measures, taken from such varied sources as Bloomberg, Chicago Board Options Exchange, the Debt Management Office, London Stock Exchange, Merrill Lynch, Thomson Datastream and the Bank of England itself.
The story from the index is plain enough. From 2002 onwards, liquidity became abundant, and this led to a surge in asset prices that is now so cruelly unwinding.
Then came the great falling off after the summer of 2007. However, until the Lehman bankruptcy the extent of liquidity tightening was broadly comparable to the dot.com crash. After Lehman, conditions deteriorated dramatically, and despite the enormous efforts of central banks, things haven't yet begun to improve.
Just for the record, the last datapoint for this series is October 17.