The key moment came in the mid-90s, when British law was modified to allow American lawyers to go into partnership with English lawyers. Since then, American firms have been flooding in and show no signs of slowing down. While a few English law firms might harbour ambitions to open offices in New York, their colonial proclivities pale in comparison to the Americans', as the number of American firms doing business in London now tops 100. The top 50 of these, according to London law magazine Legal Businesss, now employ more than 3,000 lawyers in the capital alone -- 2,200 of them English qualified. It's no secret that the aggressive American firms have a comparative advantage: a lot of money to throw around.

The six so-called Magic Circle law firms in London are, in order of turnover, Clifford Chance, Linklaters, Freshfields Bruckhaus Deringer, Allen & Overy, Slaughter and May, and Herbert Smith. These are the firms widely recognised as dominating the corporate work and advising on the highest value litigation and capital markets transactions. All six have had to focus on raising their profitability levels in the wake of the economic downturn following the dot-com crash and the terrorist attacks of 11 September, not least to keep their partners happy in the face of tempting offers from the Yanks. The result has been a paradigm shift: like their U.S. counterparts, there is an increasing focus on the dreaded billable hour. Lawyers are expected not only to log the hours, but to be on call for clients day and night. Annual targets of 2,000 billable hours are not unusual as the days of long lunches and carrying less productive colleagues have become a thing of the past.

The Americans can afford to pay more because they are, by and large, more profitable businesses. A part of the reason for American firms' relative success is that they haven't made the extensive overseas investment that many top English law firms have. A larger reason lies in the U.S. litigation culture and its mind-boggling revenues. Of course UK firms do litigation, but it's a smaller part of their business, constituting 10-20 percent within the Magic Circle. This would be highly unusual for a major American firm, as it is typical for half of a U.S. firm's lawyers to work solely on the contentious side of the business. Of added significance is that litigation is not only profitable, but counter-cyclical;, when capital markets and M&A were quiet at the start of this century, American law firms saw no dip in revenue while UK firms suffered. Even when businesses aren't merging, absorbing and raiding one another, companies love to sue -- which means a steady flow of cash to the firms representing them.

Last year was a banner one for U.S. firms doing business in London. According to The Lawyer, virtually every American law firm saw solid to stellar performance in '05. Debevoise & Plimpton, for example, posted an unprecedented 67.5 percent increase in revenue coming out of the London office (accounting for 10 percent of Debevoise's total revenue in 2005). LeBoeuf Lamb Greene & MacRae reported similarly impressive earnings, marking 2005 with a 43 percent rise in UK revenue. Meanwhile, Shearman & Sterling's UK partners took home, on average, ??950,000 -- not a great leap over 2004's figures, as The Lawyer reports, but still 20 percent higher than the global average for profits per equity partner (PEP). Dechert partners also had some cause for celebration, as 2005 saw the firm's UK revenue climb by 15 percent and UK PEP leap nearly 30 percent to ??846,500. White-shoe Wall Street firm Simpson Thacher boasted a 30 percent rise in UK revenue. Impressive numbers like that (with equally impressive profits per equity partner) will surely demand the attention of both English lawyers and their employers -- English firms.

When it comes to the war for talent in the London market, U.S. firms take a different approach to partner compensation, which has attracted some of the England's top advocates. As a rule, Americans pay partners according to how much work they generate (a.k.a. the 'Eat what you kill' rule). The largest UK firms, on the other hand, pay partners according to seniority. This means that the highest-billing at English firms (rarely the most senior, rarer yet the highest-paid) would be better off parlaying their professional zealotry into higher earnings at a U.S. firm.

There are other factors luring English attorneys to American firms, of course. As The Lawyer reported in March 2006, the recent defection of two high-level Linklaters private equity partners to Chicago-based Kirkland & Ellis seemed linked to tension between Linklaters' private equity team and its banking group. Kirkland, operating through a headhunter (who, according to The Lawyer, blabbed about the move months in advance), capitalized on Linklaters' internal strife, taking Graham White and Raymond McKeeve -- along with a portable book of clients including CVC and TDR Capital. The move demonstrates that American firms -- which, being comparatively new to the market, are freer to try new things -- may be more willing to accommodate disgruntled attorneys' professional whims than traditional UK firms.

All of this means that for a talented lawyer entering London's legal market, U.S. firms offer a viable -- and rather lucrative -- alternative as a place to begin a career. However, you would be gravely mistaken to think you can make a killing working at an American firm without putting in American hours. As a result of the whizbang billable ethos, all of the law firms in London (American and English alike) now expect their associates to earn their keep, and then some.