Chiltern Railways trains from Banbury have been disrupted following signalling problems.
The fault at London Marylebone Station occurred at about 5.30am and has now been fixed but delays are expected until at least 10am.
A number of services from Banbury have been hit by delays, with the 8.47am service to Birmingham Moor Street cancelled, as well as the 9.06am service to Birmingham Snow Hill.
The 9.33am service to Newcastle via Doncaster and the 9.46am service to Birmingham Moor Street have also been cancelled.
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