London Briefing: Schemes designed to rip off consumers have been around for as long as anyone can remember and most of them are well known.

The amazing thing about many of these scams is how they keep fooling people: snake oil salesmen may have been around for the last couple of centuries, but they still seem to be able to find gullible customers eager to snap up the nonsense that they are peddling.

The two tried and trusted tactics of the con artist are: first, an appeal to our greed and, second, to our vanity.

Snake oil was originally claimed to cure a range of ailments, including plague and baldness.

Pyramid selling, one of the oldest financial scams, always finds a willing audience among those whose greed is matched only by their ignorance of basic arithmetic.

Modern-day frauds often have their roots in many of the schemes of old, with the added gloss that is imparted by the use of technology.

Few conmen have to show their faces these days: they can hide behind the internet.

The application of technology to the old basic principles means that we are now assailed on a daily basis. On Easter Sunday, two different fraudsters phoned me, each registering as an overseas call.

The first tried to persuade me that I had won a free holiday; all I had to do was to arrange an appointment to sort out the details.

My guess is that this will turn out to be a variant on the old time-share sales pitch.

My holiday will turn out to have conditions attached that will make it worthless and I will have to sit through a high-octane sales presentation for wonderful time-share apartments somewhere in Costa del High Rise.

The second call was another attempt to appeal to my greed.

The nice-sounding man claimed that I had previously entered a prize draw - which I had subsequently won - and that his company had tried repeatedly to contact me to ensure that my prize could be delivered safely.

That prize was yet to be determined, but would be either £1,000 (€1,452) cash, a convertible Jaguar sports car or another significant cash sum.

All I had to do to claim my prize was to call a premium-rate number, costing £1.50 a minute.

What sentient human being, I mused, would fall for either one of these lunacies?

The answer, surprisingly, is that quite a few people dial that premium-rate number and end up being shocked when their significant cash prize amounts to less than the cost of the call.

More sophisticated frauds now seem to focus on identity theft of one kind or another.

Anyone logging on to their British bank account these days has to negotiate several warning screens about "phishing" e-mails that purport to come from, say, Lloyds TSB, requesting confirmation of account details and, crucially, passwords.

While such scams should now be familiar, the latest version is more sinister: "pharming" involves the creation of websites that replicate the legitimate log-on page for your internet bank.

Once you have entered the necessary details, the thief is potentially able to use them to raid your account.

The British government has issued guides to a lot of these scams and has repeatedly warned consumers about their dangers.

The British department of trade and industry devotes a significant chunk of its website to detailing the most common frauds.

The infamous "West African" or "419 Advance Fee Fraud" is given a lot of attention. I'm tempted to think that nobody falls for this one anymore, but I get at least one of these kinds of e-mails a month.

Somebody clearly thinks that there is some mileage left in this one.

The department's Prizewinner Or Prize Fool downloadable leaflet explains "how to avoid becoming a scam victim and the warning signs to watch out for".

The title says it all. That the department has to spend so much time and money on this kind of thing is testament to the ingenuity of the fraudsters and, perhaps, the gullibility of many consumers.

For most people, the cost of all of this is measured in terms of intrusive phone calls and annoying e-mails, but the real mystery is why the scam industry is so vibrant: it can only be that loads of us still fall for snake oil.

Chris Johns is an investment strategist with Collins Stewart. All opinions are personal.