I suppose the fact that many of our towns and cities now house a variety of different-sized industrial museums provides the hardest possible evidence of the structural shift in Britain's economic activity over the past half-century.

Great swathes of the world's first industrial nation have gradually changed; once buoyant manufacturing bases have become little more than assembly plants, while an increasing number of urban areas accommodate converted factories, symbols of a former glorious era, now open for visits by wide-eyed schoolchildren.

During the recent half-term holidays, my brother and I took a brood of Sharkey youngsters (and others) to one such industrial museum.

Among the marvellous collection of machines, railway carriages and an outstanding area devoted to the seafaring trade sadly politicised to reflect the contemptible one-sided views of the local council's PC-brigade I was struck by advertising's burgeoning role in the economic cycle.

Bold monochrome posters urged consumers to eat this or drink that, while finely-coloured thin metal sheets extolled the virtues of everything from soap to petrol in basic, almost naive fashion.

Advertising has become more sophisticated over the course of the last century or so, although it is striking that several of the products and companies that had the foresight to promote their wares to an increasingly wealthy population are still with us.

You can be sure of Shell' was one such memorable strapline which peered down from above a finely-preserved Morris Minor.

The youngsters were astonished when my brother and I explained that yes, when we were their age, we would happily tootle along for miles in the back of our MM', without a DVD, iPod or PS2, just bombarding our parents with a constant flow of questions and chatter.

But before disappearing down memory lane, our visit to the industrial museum, which allowed us to briefly wallow in Britain's past, also thankfully re-affirmed that good companies such as Shell stay around for a long, long time.

In other words, quality lasts. It is an adage with which we are all familiar, but during uncertain times for investors, it is one well worth remembering.

Share prices in an uncomfortably large number of companies have taken a hammering since the beginning of May, but investors committed to equities for the long term should consider whether this represents a buying opportunity, particularly of quality stock.

Whenever share prices motor to a new peak, as they did towards the back end of April, danger is rarely far away, as most investors who experienced the bursting of the dotcom bubble in 2000 will testify.

The same thing happened in 1987, when the market lost 30 per cent of its value between July and October. Two years later the share index recovered, yet investing in quality when the market collapsed in October 1987 was a smart move.

Bold investors had made average gains of 45 per cent by the time equities picked up again in 1989.

I have recently topped up my holdings in companies such as Tesco and AB Foods, organisations that display the type of intrinsic strength which suggests that, like Shell, they will be around for a long time.

Who knows, visits to industrial museums in 40-50 years although they will probably be called social history centres' by then will permit youngsters to examine items such as the first Tesco carrier bag.

One other thing is certain they will almost certainly be able to see those You can be sure of Shell' signs too, without having to ask who Shell is, or was.