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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The UK drivers' train union ASLEF has offered to suspend next week's strike action. It comes as fresh talks to end the dispute are agreed.
Tuesday afternoon's weather for the east of the region
Tuesday afternoon's weather for the west of the region