The practice aims to use London as a base from which to win business in the UK and, in the longer term, expand into central Europe. It hopes to land contracts for ports, stations and airports in this area, as it did in the Middle East in the 1970s.
Staff numbers at the London office have risen from 60 to 140 in the last two years.
Mark Regulinski, managing director of the UK office, is one of three executives who have come over from the USA to spearhead the operation.
He said: "The lion's share of our work in London now is for non-American clients. Before, when we were designing Canary Wharf, the strength of the London office was based on American financial and legal clients and it was very much tethered to Chicago and New York. We've never had to be a force on our own until very recently."
This is the first time that the London office has had a complement of five directors, three of whom are top-level partners. Regulinski and technical director Kevin Peters, both formerly of the New York office, were moved to London earlier this year. Design director Larry Oltmanns came from Chicago in 2000.
At present, two-thirds of the workload is for UK projects, mostly in London, but SOM aims to win transport contracts in former Eastern Bloc countries such as Poland, which are applying to join the European Union. To date, the office's only firm transport order for a European project is the redevelopment of Dublin airport.
Major projects under way in the London office include a 150,000 m2 mixed-use development for central Lisbon, a 40-storey office tower for Warsaw and two office buildings in the City of London for developer British Land.
In addition, the practice is putting increasing emphasis on design competitions, and has been shortlisted for Nato's headquarters in Brussels.
It was also confirmed this week that SOM will draw up a masterplan for the land behind Euston Station in London, which is set to be developed by Railtrack.