"The Good Doctor" wrote

Evergreen 2 was carried out by John Laing Group on a Design, Build,
Finance and Transfer basis. John Laing Group funded the project and
took full commercial risk. However the assets became the property of
Network Rail, because that is the way the franchise system works,
Chiltern Railways being effectively prevented from owning such
assets.

AIUI Chiltern do own a couple of infrastructure assets, including Warwick
Parway station and the 'new' platform at Princes Risborough.

Peter