Complex sentence: Whilst at Granada Television, he was asked to be the temporary announcer of "University Challenge" for the 1997 series, and then returned permanently in 2001 and has remained the voice of the programme to date.
Split into simpler sentences: Whilst at Granada Television, he was asked to be the temporary announcer of "University Challenge" for the 1997 series, and then returned permanently in 2001. He has remained the voice of the programme to date.