And it is burgeoning. All the Big Six and most of the next tier have substantial forensic accounting departments and they have recently been joined by a couple of new specialist kids on the block - one of them the European headquarters of Canada's largest independent financial investigators.
"Litigation support work has been going on for years," says Rick Helsby, partner in charge of forensic accounting at Coopers and Lybrand. "But given the fact that we are now in a much more litigious climate, the call for forensic accountancy has dramatically increased over the past four to five years and this trend shows signs of continuing." His firm now employs 50 in London and half that number in the regions.
"It's a curious area because although all the big firms use the phrase 'forensic accounting', people often ask what it means. I would describe it as being all about the resolution of disputes. When you have two warring parties, the role of the forensic accountant is to provide expert business advice which will support one party's case."
Forensic means literally "connected with or used in courts of law", though of course a vast majority of cases settle out of court. The brief is wide and may involve estimating loss of profits in contractual disputes and insurance claims, fraud investigations of all kinds, tax and duty work, money tracing, competition matters and business valuations.
Much of the work is international on a US/UK/European axis and practitioners stress the importance of a sound contact base overseas. One firm of forensic accountants was called in by an Eastern European government after the collapse of Communism, to trace the millions spirited out of the country by its former head of state. Staff travelled half of Europe in their search.
Not all jobs have this glamour. Forensic accountants may be called in before a fraud is even alleged as when Coopers was asked to computer scan the National Power/PowerGen share issue for possible multiple applications. Instructions come directly from the client or through solicitors. If a case reaches court the accountant will appear as an expert witness.
The huge rise in fraud over the past few years has accounted for much of the growth in business. Martin Foster, UK head of forensic accounting at KPMG, lays some of the blame for this rise on the pressure on employees to perform. "Corporations take layers out of management and that tends to open up opportunities for people to beat the system. Sometimes this is for personal gain but sometimes there is no direct benefit other than the appearance of delivering better results to bosses than is actually the case."
To deal with the investigations side, most firms have brought ex-policemen on board, often of senior rank. If the services of an investigation agency are needed, it is their job to supervise the agency's work. However, because this is a totally unregulated field, a couple of practices have decided to establish a formal link with a particular agency in order to ensure control, confidentiality and conformity of standards. Others are considering following suit.
For the first few years of the forensic accounting boom, the Big Six had it pretty much all their own way. Martin Foster of KPMG emphasises the value of being able to draw on specialists from other departments in the firm. "It is very useful to be familiar with particular types of investigation or certain areas of industry so you know exactly what you are looking for. You also need investigative and interviewing skills, tenacity and an eye for detail."
So can the two newcomers on the scene compete? Definitely, says Monica Bond, who heads the new London office of Lindquist Avey. "I can draw on the resources of any of 250 specialist forensic and investigative accountants in the Lindquist Avey group internationally and I complement the permanent staff in the London office with consultants who are specialists in a particular field on an ad hoc basis.
"The advantage of a specialist practice is that while auditors look at the figures, we look behind them. I see it from the instructing solicitor's viewpoint. They need specialists within the specialism." For this reason Ms Bond has taken on experts in white collar crime, intellectual property, tax and customs and computers - and is planning to expand her team.
David Lee at Lee and Allen is aware that as a small niche practice his firm lacks the infrastructure of its competitors. "On sheer numbers we can't compete and nor would we want to. We are very case-driven: we are not interested in managing a great big body of people." To acquire the necessary breadth of experience, the firm - launched last year by David Lee, former head of special investigations at Price Waterhouse, and his colleague Tim Allen - has set up a banking panel composed of independent consultants with expertise in different fields including derivatives, foreign exchange and investments. "This gives us great flexibility. It is more powerful than being tied to people in-house."
Clients may prefer to use their own accountants for forensic work, says Rick Helsby of Coopers and Lybrand. "A client's own accountant will already understand the needs of his particular business, which somebody called in by a solicitor is unlikely to do." However the truth - as Mr Helsby admits - is that his firm is unable to take on between 20 and 40 per cent of the forensic work it is offered because of conflict of interest.
It was precisely this problem which led to the departure of Messrs Lee and Allen from Price Waterhouse. David Lee says: "It was very frustrating being asked by regulators, prosecutors or lawyers to act only to find that we were conflicted out because some of my partners were offering litigation, tax or auditing services, or selling them computers. Our aim is to be the seventh alternative for this sort of work, behind the Big Six. Because we can work on an unconflicted basis we believe there is ample room in the market for us."