The actress, 71, said: “We were supposed to be going from Venice to China but then China refused to let us in.
“I don’t know why as we don’t make political programmes.
“However, they pulled the plug.”
The exhaustive trip had been three years in the planning and was a dream come true for Joanna.
The Silk Road shaped the modern world, bringing silk, printing, spices, gunpowder, and many other things to the West.
The four-part series, which begins at 9pm on Wednesday, sees Joanna travel through a breathtaking array of landscapes following in the footsteps of the merchants, conquerors, kings and pilgrims who once lived and died along this route.
Joanna added: “It was my idea – and one I’d had for years. Many years ago, my maternal grandparents travelled along the Silk Road as my grandfather was a diplomat.
“I wanted to follow in their footsteps. Then China refused to let us in but Iran said yes.”