Prince Harry has helped break the world record for the biggest currency trade, by taking the call to complete the deal on Monday.

Harry who is third in line to the throne, closed a foreign exchange deal worth  18 billion euros ($A23.57 billion) at brokerage firm BGC Partners’ charity day in London.

The 26-year-old army helicopter pilot chatted down the line to a trader from Barclays, using trading floor jargon.

Robert Sully who is a broker on the foreign exchange desk handed the phone to the prince describing his performance as “brilliant”.

“We told Harry to say ’28 your choice’, which means you can buy or sell,” he said.

The planned trade went through and the BGC trader described it as the biggest forward foreign exchange deal in history.

The previous record was set by Harry’s elder brother Prince William, who completed a foreign exchange trade worth 17 billion euros ($A22.26 billion) at a different brokerage last December.

All revenues made during the charity day are donated to 29 good causes.

Harry was joined by celebrities including Rolling Stones guitarist Ronnie Wood and singer Sophie Ellis-Bextor.

The army captain chatted with Czech supermodel Eva Herzigova, who was also trying to complete a deal.

The BGC fundraising day is in memory of staff from its sister company, investment bank Cantor Fitzgerald, who died in the September 11, 2001 attacks in New York.

The firm lost 658 employees which is more than any other organisation in the twin towers.

Harry was attending on behalf of Sentebale, the charity he co-founded with Lesotho’s Prince Seeiso to help orphans in the landlocked, AIDS-ravaged southern African country.