The All-Share index is now below its 10-month average. This matters because as Mebane Faber of Cambria Investment Management pointed out in an influential paper back in 2007 a simple policy of buying an equity index when it is above its 10-month average and selling when it is below it has succeeded for years. He's estimated that since 1901 this rule has given higher returns on the S&P 500 than a simple buy and hold strategy, with significantly less volatility.
But would such a rule have worked in the UK in recent years? The answer is yes: partly.