A survey of legal salaries published today reveals that US firms in London are paying almost double what their City counterparts can offer.
The average wage for a seven-year qualified assistant in a US firm based in London is u100,000, compared with between u52,500 and u60,000 on offer at City firms.
The survey shows a sliding scale depending on experience. But the amount offered by US firms remains roughly twice that of UK firms.
The report, compiled by recruitment consultancy QD Legal, is based on a survey of 500 firms and 500 companies.
Adrian Fox, director of QD Legal, says: "UK firms are trying to close the gap, but they are not succeeding.
"US firms are constantly upping the ante. The upshot is that US firms' wages are continuing to outstrip those in UK firms."
Attached to the report, which costs u295, are extracts of a survey by The Lawyer and QD Legal on what attracts lawyers to particular types of firms.
Almost 70 per cent of lawyers see money as the prime motivating factor.
But increases in salaries will only keep a lawyer at a firm if they think there is not an underlying problem with the firm.
Figures suggest that 50 per cent of lawyers would consider working for US firms because they pay so well.
But more than 60 per cent of respondents say an unattractive feature of US firms is that they have a "ruthless" culture based on working hard and being unsympathetic to problems.
Some lawyers see quality of life as the greatest motivator for working at a particular firm. Many of these are attracted to regional practices where some lawyers are paid a third of what they would earn at a US firm.
But the report says: "Quality of life issues are a bit like religious faith. If you are a believer they are often a prime motivator. If on the other hand you think that you end up working much the same hours for less money then quality of life issues are unlikely to sway you."
Fox says: "Our report is the most comprehensive ever. It is the first of its kind.
"But we intend to make it an annual benchmark for lawyers to compare their salaries."