From auction houses to accountants, estate agents to jewellery dealers - anyone working in a field which handles large amounts of other people's money will find themselves drafted into efforts to crack down on dirty money.

The new obligations are the result of the Proceeds of Crime Act 2002, which brings new European regulations into UK law.

Law enforcement experts set the amount of laundered money sloshing around the UK at as much as �50bn every year

It extends the duty to tell the National Criminal Intelligence Service (NCIS) about suspicious behaviour by clients far beyond the banks, building societies and other financial institutions on whom it rested most heavily till now.

It also means high-cash businesses must register with Customs and Excise.

So from 1 March, anyone walking into a car showroom flashing �100,000 in cash, claiming a �10,000 business expense without the proper paperwork, or showing reluctance to provide a name and address at an auction may become the subject of a Suspicious Activity Report (SAR).

Rules - or guidelines?

But what, exactly, counts as suspicious?

TO REPORT OR NOT TO REPORT? All high-cash businesses have an obligation to report, but those most likely to be affected include: Accountants Antique dealers Auction houses Car dealers Casino operators Estate agents Jewellers Lawyers Others potentially on a launderer's hit-list: Betting shops Gyms Mini-cab firms Nightclubs Restaurants

No-one is completely sure - and the absence of the codes of practice which the government promised is not making life any easier.

With prison the ultimate sanction against anyone failing to file a report when they should, many businesses are running slightly scared.

For a start, the new rules expand the definition of money laundering to any transaction which involves handling the proceeds of crime.

In addition, the old assumption that only amounts over �10,000 are suspicious is now a thing of the past.

And the net is drawn pretty tightly: even a client who simply appears to have paid for a job in cash to avoid VAT should, in theory, be reported, on pain of a hefty fine and a jail term of up to two years.

The result, some fear, could be a flood of "defensive" reports heading for NCIS, drowning the agency in a sea of paper.

High-cash businesses such as casinos are launderers' targets

There is evidence to suggest it is already facing a huge backlog of unread reports.

A report by accountancy firm KPMG, commissioned by the government, revealed last summer that NCIS's existing backlog would almost double from 58,000 to more than 100,000 reports by 2004, although it said the agency was making progress.

No-one in the trade wants that to get any worse.

Not all bad

But there are optimists out there.

For a start, many argue that the new rules are only making businesses take responsibility for their own actions.

Money launderers are increasingly shifting their attention away from the formal financial institutions where the pressure from the Financial Services Authority to identify clients has built in recent years.

And those who provide the funding for terrorism are doing much the same thing.

Few deny that high-volume, cash-rich businesses have become the vehicles of choice for washing dirty money.

Help wanted

So in the property trade, for instance, the Royal Institution of Chartered Surveyors says it has drawn up rules for estate agents to follow, including the simple requirement to check names and addresses of cash-based clients.

Similarly, the Institute of Chartered Accountants has been negotiating with the Treasury to work out just what is expected of its members - although it has still to settle the question of "privilege" attached to discussions with clients.

Jewels also offer an inflation-proof store of value for criminals

Experts such as David Winch of forensic practice Accounting Evidence Ltd say they are reasonably happy with the way things are, even if they would like firmer, more explicit rules sooner rather than later.

A report should be based on "reasonable grounds for knowledge or suspicion", Mr Winch says.

For any business swept up in the new rules, that could mean unusual or unexplained factors, not simply evidence of lawbreaking.

But that does not mean that experience and knowledge should be set aside in favour of a knee-jerk approach, he says.

Each organisation will need a single person responsible for dealing with these issues.

This Money Laundering Reporting Officer can take the advice of colleagues, and then make a judgement as to whether to report or not.

Teething troubles

Be that as it may, no-one is pretending the new system is entirely straightforward.

There are likely to be hiccups.

NCIS may well be swamped.

And worries about the conflict between duty to clients, and duty to act if law-breaking is suspected, will not go away in a hurry.

But law enforcement experts set the amount of laundered money sloshing around the UK at as much as �50bn every year.