Yesterday night's visit was the couple's first joint visit to the building -- after their engagement in October last year -- where they will walk down the aisle on April 29, the 'Daily Express' reported.

The couple spent an hour-and-a-quarter inside the Abbey. Prince Charles joined them for the performance to help them make a final choice of music for their great day.

The three arrived at 8 PM and were sneaked into the Abbey via a back gate in Prince William's father's dark-blue Jaguar, leaving via the same gate at 9.15 PM, the newspaper said,  quoting a royal insider as saying.

The royal insider said William and Kate were in London last night especially for the performance. "They looked relaxed and seemed to enjoy themselves. They are obviously very keen that everything should be right on the big day."

A full orchestra practised for an hour-and-a-half before William, Kate and Charles arrived. About a dozen young choristers wearing black velvet cloaks paraded into the Abbey in formation.

Another senior royal source said: "William and Kate listened to some of the music that will be played at the wedding, but not all of it."

He confirmed that part of the reason for the couple's visit last night was to choose which music would finally be used. "That was part of the process. The orchestra also had a few pieces that they had wanted the bride and groom to hear."

He revealed that Prince Charles had advised the couple on their choice of music. "They have sought his advice and involved him in the decisions," he added.