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.
More top news
The decision not to press charges in the abuse case against Sir Cliff Richard is being reviewed.
The morning sunshine will be replaced by more cloud and perhaps a little rain later.
Cloud and occasional light rain or drizzle spreads eastwards through the morning.