IF you watched the Channel 4 show The Piano at Christmas, you will have spotted Woolton Hill singer and composer Fiona Bennett. The Christmas special invited some of the favourite pianists from series one of The Piano to return to play festive numbers in front of commuters in London’s King’s Cross Station When she appeared in the first episode of the new series of The Piano, she performed one of her own compositions on the St Pancras Station piano. Little did she know that there were two well known musicians watching and listening from a secret location. “When Claudia Winkleman told us all we’…