Video: 86 per cent of Chiltern trains ran on time over the past 12 months. Southern Trains were below average with 55 per cent punctuality. Less than half of Virgin and Cross Country trains were on time.
There are delays of up to 40 minutes on trains running from Oxfordshire into London Marylebone.
Chiltern Railways says this is due to problems with line side equipment between Beaconsfield and High Wycombe.
Services from Aylesbury in Buckinghamshire are also affected.
Normal rail service resumed on Chiltern Railway between Banbury and Bicester North following earlier electrical supply problems at Kings Sutton