Complex sentence: The school grounds were sold to property developers for an undisclosed sum in 1997, however, the sale was overturned by the Charity Commission following significant pressure from parents and former students who claimed the land was undersold.
Split into simpler sentences: The school grounds were sold to property developers for an undisclosed sum in 1997. The sale was overturned by the Charity Commission, however, following significant pressure from parents and former students who claimed the land was undersold.