The Prince of Wales was asked if he could be kidnapped and held for ransom as he met Poppy Appeal volunteers and celebrity supporters.
Charles greeted those working to raise money on board the London Poppy Day red bus at Clarence House as part of the campaign to raise £1 million in a single day from donations across the capital.
TV presenter and Poppy Day ambassador Ben Shephard said Charles spent some time joking and laughing when he boarded the Routemaster.
"We thought we could try and drive off with him on the bus and launch a ransom to raise more money," Mr Shephard said. "But he thought we wouldn't get very far."
Charles also joked about having a sing-along on the bus and riding a Harley Davidson before meeting bikers from the Royal British Legion Riders Branch.
The Prince then met volunteers inside Clarence House's Poppy Day counting room, where the money raised is rapidly counted in machines.
Hundreds of volunteers have the important job of tallying the funds at five counting stations across London including, for the first time, the one at Clarence House.
Richard Atkinson, a banker and volunteer counter at Clarence House, said Charles wanted to know how the money counting machines worked.
"He was very intrigued and tried to understand the logistics of how this final part of the process works," Mr Atkinson said. "He was also very interested to know what we all did as day jobs as well."
This year the volunteers, representing the Army, Navy, RAF and a host of companies, aim to raise £1 million in a single day across the capital, more than twice what was raised on London Poppy Day 2011.