Any sign of an approaching end to the support offered by governments to the global financial system - low interest rates, quantitative easing et al - is guaranteed to spook investors, who are already starting to wonder whether the market has got a little ahead of itself.
So news that China has raised banks' reserve requirements by 0.5% - what some economists see as the first step in tightening monetary policy - has seen the UK market's fall accelerate. The FTSE 100 is now down 70.04 points at 5468.03, with US futures predicting an opening fall on Wall Street of a similar amount.
The Chinese move comes after its buoyant trade figures, and it designed to head off inflationary pressures. So far UK and US central banks have maintained their stimulus packages, but their every pronouncements are scrutinised for signs that the easing may be ending. The Bank of England is also buying long dated gilts during this trading session.
