Complex sentence: Shelley has said that that following the operation he finds it hard to simultaneously sing and play bass guitar for long periods; nevertheless, he currently plays bass (with occasional backing vocal duties) in rock and pop covers bands based in South Wales.
Split into simpler sentences: Shelley has said that that following the operation he finds it hard to simultaneously sing and play bass guitar for long periods. Nevertheless, he continues to play bass (with occasional backing vocal duties) in rock and pop covers bands based in South Wales.