Lawyers have made 'fly-in fly-out' - the practice of visiting foreign countries where their firm does not have an office and advising clients from hotel rooms - into a £1.6bn business
The Law Society, which produced the figure from international trade statistics, has also identified numbers of lawyers who use tourist visas to gain access to countries in which they are working.
Lawyers use fly-in fly-out either because the jurisdiction in question does not allow them to provide UK and other foreign legal advice from a base in the country, or because their firm has not set up an office there.
According to the Law Society, the fly-in fly-out industry has grown by nearly 100 per cent in the past two years.
Law Society chief executive Janet Paraskeva said: "It is difficult to know exactly how many lawyers are involved and how often they travel on tourist visas because of the trade limitations on lawyers crossing borders to deliver advice."
Lawyers involved in fly-in fly-out blame the fact that many countries, such as Korea and India, have not liberalised their legal markets in keeping with the free movement of international trade.
In the present round of World Trade Organisation talks, 50 out of 144 countries have expressed an interest in examining greater liberalisation of their legal services.
"The ongoing strength of City firms in London depends on, to a great extent, continuing to open up markets abroad - the current talks are our most promising avenue for making progress in key markets, such as Korea and India, where solicitors find it virtually impossible to work at present," Paraskeva said.