It is a sad fact for investors and tipsters alike that, just as nobody sounds a siren when stockmarkets peak, no one rings a bell at the bottom either.

But as Anthony Bolton, Fidelity’s celebrated stockpicker, observed this week, we do have a reasonable proxy for spotting the trough: the moment when the best performing sector of the last few years starts to lag the worst performer. In this case, that means the moment at which the stockmarket starts to favour financials - for which read banks - over miners. “That’s the key switch”, said Mr Bolton.

That long-awaited trade carries echoes of the top of the millennial bull market, whose zenith was signalled by investors’s abandonment of the new economy for the old - when tobacco stocks started to outperform telecoms. In March 2000, it was right to have sold Vodafone and bought British American Tobacco, and it has been ever since.

So when, this time round, should investors sell Rio Tinto and buy Royal Bank of Scotland? The reverse trade has been the profitable one for the last two years, just as owning Vodafone and selling BAT was in the two years preceding March 2000.

But that duration provides no indication that the bottom is near. Richard Crossley, the closely-followed technical analyst at NCB stockbrokers, points out that the trends of the last few years remain very much in place. “There is no sign of any deterioration”, he says.

That is a blow for all those that suggested that BHP Billiton’s bid for Rio was top of the market stuff in the tradition of Vodafone’s bid for Mannesmann. Indeed, the mining sector is up 20 per cent in the last two months alone. Further, although miners have now outstripped the telecom stocks of the late 1990s in performance terms, there is no indication of a bubble. Citigroup notes that valuations have simply kept pace with earnings.

That suggests that taking profits on what remains London’s preeminent stockmarket sector remains premature.

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