Man Group, the financial services company, has created the world's biggest independent futures broker through the £100m acquisition of GNI.
The cash deal, confirmed yesterday, will give Man Group a greater number of daily transactions than most derivatives exchanges.
Kevin Davis, the managing director of Man's financial services business, said: "There's not much competition left [in Europe]. It was us and GNI [in this market]. Now we've bought them.
"We were already larger than Liffe [London International Financial Futures Exchange]. Now we've overtaken the Chicago Board of Trade."
GNI was off-loaded by Old Mutual so the South African group could focus on its core insurance and fund management business. It is also trying to sell Old Mutual Securities but that transaction hit difficulties when Beeson Gregory walked away from talks.
The GNI acquisition will boost Man's share of the retail market, especially in equity and interest-rate derivatives. Mr Davis said GNI also provided propriety technology for trading.
"You should not expect a further significant brokerage acquisition from us, as we bed this down and make sure that one plus one equals three," he said.
In the six months to 30 June, GNI made a pre-tax of £5m. Mr Davis said the deal would yield costs savings of £8m a year but there would not be significant redundancies among GNI's 500 staff.
Man shares closed up 5 per cent at 990p.