A secret piece of music hidden in carvings at a famous medieval chapel in Midlothian might have been found by a father and son team from Edinburgh.

For more than 500 years, a musical code has been locked in the stones of Rosslyn Chapel. Now Stuart Mitchell, 41, and his father Tommy, 75, say they have deciphered it and will perform the music in May at a concert in the 15th century chapel.

Following its appearance in Dan Brown's novel The Da Vinci Code, numbers of visitors to the chapel have increased rapidly.

Stuart Mitchell discovered a series of figures which he calls an "orchestra of angels" at the base of elaborate arches round the altar, with each angel holding a musical instrument.

He worked with his father to decipher the patterns on cubes which jut out from the arches.

According to Tommy Mitchell, the markings concealed a tune which they were determined to crack.

He said: "We were convinced from the position at the top of the pillars of the angels and they are all directly under the arches where the cubes occur that there was music there.

"We got clues from other books as well. Over the years this became more of an obsession than anything else and we decided we had to find out what was going on."

"If these patterns and cubes had not contained music anything we turned up would have been purely random and would not have sounded hauntily beautiful."

Stuart Mitchell said the tunes could have been hidden because knowledge of harmonics may have been seen as dangerous, even heretical, by 15th century church authorities.

He said: "What we have here is a recorded piece of music, it is almost like a compact disc from the 15th century."