Lancaster was joined by Girls Aloud singer Nicola Roberts and Spandau Ballet frontman Tony Hadley to work as traders in London's financial district for the 6th Annual BGC Charity Day, swapping places with staff to man phones on the trading floor.
The firm's bosses annually commemorate the loss of hundreds of colleagues at their affiliate company Cantor Fitzgerald who were killed after Muslim extremists flew two planes into the World Trade Center in 2001.
Lancaster says, ""The buzz on the trading floor was amazing... It's fantastic to think everyone at BGC Partners has given up their time for free and to be generous enough (sic) to give the day's revenues to charity.""
Across the Atlantic, Duff turned up to help the cause by manning phones at BGC's New York office.