Mr Archer, 24, and two of his colleagues at Credit Suisse First Boston were suspended earlier this week pending investigations into possible manipulation of trades on the Swedish Stock Exchange.Swedish authorities say their financial police and criminal courts could become involved.
The alleged irregularities are thought to involve sharebuying in Stora, a Swedish pulp company, and possible "market manipulation".
Mats Wilhelmsson, head of market surveillance in Sweden, said: "The sums are not really relevant, but the actual trades are. There were trades that led to one in particular and the value of these trades was around [pounds 500,000]."
He said he could reveal no details of what was alleged to have been wrong with the dealings because of the possibility of prosecutions.
Mr Archer and his suspended colleagues, David Crasanti, 34, and Adrian Ezra, 31, are in a group of "index arbitrage" traders known as the "Flaming Ferraris" because of their penchant for pounds 14 cocktails of rum, calvados and blue Curacao.
They exploit tiny anomalies between index prices and futures contracts, placing bets of up to pounds 3bn to make worthwhile profits. They - and 13 colleagues spread around London, Hong Kong, America, Europe and Australia - are rumoured to have earned Credit Suisse First Boston (CSFB) pounds 100m last year, sharing a pounds 5m bonus.
The group, led by Mr Crasanti, a former wrestler and economics graduate from Princeton, works minimum 12-hour days under extreme pressure to capitalise on a complex system, using advanced computer programmes to identify the edge that makes a profit.
Mr Ezra, a former Indian squash champion and Harvard graduate, is said to have told a friend: "The beauty of the system is that it's so complicated few people would be able to understand the way we work."
The suspended men and their other London workers, Denis Albert and Conor Campbell, have a reputation for high living. Mr Archer is said to earn pounds 250,000 a year and have an arrogant streak.
Educated at Eton and Brasenose, Oxford, where he studied chemistry, Mr Archer was in the loutish Assassins drinking club at university. His group's nickname came from a cocktail invented by Thai Dang, who owns a Vietnamese restaurant in west London.
Thai Dang said yesterday: "They spend a lot of money and come here regularly, but they always behave impeccably."
In The Wharf, a weekly paper based near CSFB's headquarters, one ex- collegemate journalist described Mr Archer variously as a "decent, kind and clever" man.
Another wrote: "Think of the stereotype of the Oxford undergraduate, and a champagne-swigging Hooray Henry staggers into view. Double it and you're looking at James Archer."
Neither Mr Archer nor his father was available for comment yesterday.Reuse content