The US is overtaking Europe as the most important outside source of business for major City practices, according to new research that underlines the growing importance of American clients.

Fifty-seven percent of respondents to the latest Legal Week/ EJ Legal Big Question survey said that the US was the most important market for top-tier UK firms, while only 32% said the same of Western Europe.

The results, based on a survey of more than 100 senior lawyers, are a dramatic rise on last year when 48% said Western Europe was most important, against 43% voting for the US. Asia was the next most important market with 5% of votes, followed by the Middle East and Africa (4%) and Central and Eastern Europe (CEE) (2%).

Partners also said the US provides the most reliable stream of referrals for UK firms. Sixty-two percent of respondents said they receive most referrals from the US, followed by Western Europe (29%), CEE (5%) and Asia and the Middle East and Africa (both 2%).

Conversely, when it comes to referring work, the majority (62%) said most of their work goes to Western Europe with only 27% sending most referrals to the US.

UK firms also see Asia as a key market to develop, underlining the current economic revival in the region. Forty-five percent said it was the market with most potential,ahead of Western Europe (23%), the US (14%), CEE (13%) and the Middle East and Africa (5%).

David Frank, practice partner at Slaughter and May, told Legal Week: "The US market has always been the most important market for us in terms of referrals. People tend to think only of New York, but the US regionally is an important and largely untapped market."

Linklaters managing partner Tony Angel commented: "There are two areas with the greatest potential – the US and Asia. Asia is plainly incredibly important – we have been doing a huge number of deals there and there are big opportunities."

Paul Claydon, head of corporate at Morrison & Foerster in London, warned that firms expecting great things from Asia may be disappointed unless they invest in the region.

He commented: "To get work from Asia you need to be in Asia. It is strange that people have been cutting back there."