Originally Posted by Swiss Tony

They've been switching the closures back and forth in recent weeks. Sometimes the Chiltern trains run to Oxford/Bicester, other times they're running them down to Princes Risborough, across to Aylesbury then into London from there. Obviously depends on what they're trying to fix that week...

You can follow @chilternrailway on Twitter if you want. Their customer service is quite responsive through that channel FWIW.