The 79-year-old Greenspan, who steps down at the end of January as chairman of the US central bank, was heaped with praise and gifts in his final appearance as a key player at a Group of Seven conference in the British capital.

"I must say I am slightly disappointed I did not bring my flock of sheep in the hope I could shepherd them across London Bridge," Greenspan remarked to laughter at the ceremony.

The ancient Freedom confers a number of privileges, including right to take sheep across London Bridge and to walk about the City of London with a drawn sword.

Greenspan joins a select band of dignitaries who have received the award, including Nelson Mandela, Dwight Eisenhower, Theodore Roosevelt and Winston Churchill.

Greenspan, widely acknowledged as the world's most influential central banker, delivered an address on the dangers of trade protectionism and lack of budget control to a conference ahead of the formal start of a G7 session billed as partly a salute to the retiring fed chief.