I believe that any bits still held by British Railways Board Residual in 2013 that could not be passed to national park authorities or councils or other public bodies were forced into Highways England so that BR could finally be closed down. Anything with "development potential" was passed to London and Continental Railways, including some sites in Manchester, Birmingham and London.
Many of us doubted that what was then effectively an agency for motorways and quasimotorways could be trusted with historic railway routes. The ongoing vandalism of many of them, including this one, suggests we were correct. Another legacy from Cameron and O'Donnell!
And of course, doubly ironic with Great British Rail starting up, which would be a better manager for this.