Have you received a letter from a pair of clairvoyants in Geneva named "Lise and Rose" offering to predict your "winning" lottery numbers? Or an email soliciting your donation to what looks like a tsunami disaster website?

Or a phone call offering you a "once-in-a-lifetime" opportunity to invest in gemstones, fine wines or other precious commodities?

Congratulations. You've just joined a growing number of Britons who've been targeted by scammers, international conmen who use low-cost, mass-marketing techniques to part you from your money.

According to a report yesterday from the Office of Fair Trading, scams, cons and swindles originating from overseas are set to cost gullible Britons £1bn next year - an astonishing £2,000 a minute.

One of the quickest ways to run up that kind of bill - and make the scammers rich - is to answer a letter asking you to ring a premium rate 090 number in order to collect your "winning prize" in a non-existent sweepstake. A way to lose even more is to email your bank details to a man named "Roger", who purports to be the "cousin of Nigeria's former minister of finance". While you're waiting for Roger to deposit the funds in your account in the belief that you're helping him to "bribe" officials to transfer oil revenues out of the country, the conmen behind the fraud clean out your account, leaving you broke.

In the past year, the OFT, in cooperation with law-enforcement agencies in the US, Canada and Europe, have shut down hundreds of bogus telemarketers, post office box companies and internet-based investment schemes. Amid the promises they deploy as bait are winning tickets in El Gordo, the Spanish lottery, fast credit loans and investment deals involving "lucrative" properties that turn out to be derelict.

Now, in an attempt to raise awareness of the cons, the OFT has published a list of the top 10 scams and declared this month "scam awareness" month.

The most common cons include foreign lottery mailings asking you to send "administration" fees in return for a "winning" ticket; unsolicited phone calls informing you that precious gemstones are being "held" for you in secret Swiss bank vaults; Nigerian advance fee frauds that play on the email recipients' "greed"; and so-called "matrix" schemes in which punters are offered hi-tech gadgets in return for spending £20 on a low-value product such as a mobile telephone booster.