Police are warning businesses to beware of a scam which promises millions of pounds for allowing their bank account to be used.

Fraudsters then steal money from the account as part of a con which costs the UK at least £3.5 billion a year.

Brighton police say they have received a "prolific" number of reports about the letter and the town is becoming a hotspot for the fraud.

They are warning that under no circumstances should anyone reply to the letter or disclose their account details.

The National Criminal Intelligence Service, which helps MI5 tackle organised crime, fears Brighton is being targeted by organised criminals in West Africa.

The letter is sent by an author claiming to be the director of a Nigerian government agency seeking UK businessmen to act as "partners" in "providing a good company's account or any other offshore bank account" to help with transactions abroad.

The author claims Nigeria is looking for companies who can help transfer $27 million which the government is trying to repay to foreign governments.

He promises that anyone who provides a bank account for the transaction will receive 30 per cent ($8.22 million) of the amount.

The recipient is asked to keep the deal "top secret because of the nature of this business."

Once the victim has been drawn in, requests are made for payments to cover legal and administrative costs.

Some victims have lost hundreds of thousands of pounds.

Brighton police say they have been made aware of a "prolific" number of such letters in the area. Exact figures are sketchy as all letters are forwarded to the NCIS and not counted locally.

An NCIS spokesman said: "Organised crime originating in West Africa has a significant impact on the economies of industrialised countries all over the world. The main activity of these groups is fraud against individuals and companies."

The most common type of scam comes from letters like the ones received in Brighton.

The spokesman said: "We sometimes identify clusters of reported incidents.

"This happens when the fraudsters get hold of a directory of local businesses. It appears that this has happened in the Brighton area."

Estate agent Mike O'Connell, of Blakers in St James's Street, Kemp Town, is one businessman who received a fraud letter.

He said: "When I got the letter I realised it was a con straight away. I thought they must reckon I'm mad to believe this. But if someone wants to make a fast buck and gets a letter offering $8.22 million, then there are bound to be some victims."

NCIS acknowledges that only a tiny minority of people who receive the letter will be drawn in, but warns that some victims have lost thousands of pounds, encouraging the criminals to continue their fraud.

Since January 1998 NCIS has received more than a million letters, forwarded by the public and the police.

Anyone who receives a letter should send it, and the envelope, to NCIS, PO Box 8000, London, SE11 5EN.