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.
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Friday morning's forecast for the west of the region
Friday morning's forecast for the east of the region
Thursday night's weather for the east of the region