Complex sentence: It is built on reclaimed pine plantation/heathland between the M3 motorway & the main railway line to London formerly known as Railroad Heath which previously belonged to the Calthorpe Estate.
Split into simpler sentences: It is built on reclaimed pine plantation/heathland between the M3 motorway and the main railway line to London. It was formerly known as Railroad Heath, and previously belonged to the Calthorpe Estate.