Here is a depressing thought - the bear market is far from over and could have another six or seven years to run. So don't be too excited about the stunning rise in the stock market witnessed between March and June. Far from being the start of a long-term upsurge it could just be a temporary blip of good cheer.

Not my thoughts but those of Robin Griffiths, of Cazenove Capital Management, who has warned that we will not be back in a bull market until 2016.

Griffiths, one of the City's most respected chartists, dispels the notion that the past 100 years have been a period of almost unlimited stock market growth with short-term downturns to upset the positive mood. His analysis of the American stock markets - the Dow Jones Industrial and the valuation of the S&P 500 - shows that for long periods over the past century the markets lost value and the stock markets, with much volatility, went sideways.

These "bear markets" - my term, not his - lasted from 1900 to 1921, 1929 to 1949 and 1966 to 1982 - in other words a depressingly long period. And the analysis suggests we could be suffering more of the same now - and nothing that Alistair Darling does to try and reform the financial system is going to change that.

He is not the only commentator to suggest that a bull market could still be a long way off. High-profile hedge fund manager Hugh Hendry of Eclectica, for example, has been warning for some time that the stock market could oscillate or go sideways for a period as long as 25 years.

If he is right, and we've got a decade or more of tricky markets to look forward to, then it has big implications for how we invest. The approach that served investors well during the boom times of the 1980s and 1990s - buying and holding shares or funds for 10 to 20 years - is unlikely to produce the long-term profits investors are counting on. The performance of equities since 2000 is proof of that.

This does not, it is important to stress, mean that its time to dump all your shares and head for cash. Griffiths' colleagues at Cazenove are quick to point out that even when the market goes sideways for long periods there are ways to make money from equities.

However, investors and their advisers are going to have to be much more nimble in the management of their portfolio if they want to make decent returns. In an era of great economic uncertainty, investors need to pick up opportunities when they can and not be afraid to sell when the storm clouds are gathering.

One of the downsides of this approach is the extra costs you incur buying and selling on a regular basis. However, many online stock brokers will offer special deals to more active traders and fund supermarkets means that it need not be prohibitively expensive to trade in and out of funds on a regular basis. Also there is pressure on fund managers to bring down charges as we report in Vanguard launches low-cost fund range. If it's a choice between making a profit or not, the costs have to be worth taking.

Investors are also consistently warned by fund managers that timing the market is for fools. They have a point, but sticking with a investment that you no longer have faith in and appears to be heading one way only - down - is hardly a bright idea either.

Of course, predicting what is going to happen over the next decade with any certainty is prone to failure. However, the idea that we should all be taking a more active interest in our investments and finances is one that it is difficult to argue against.

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