Transport Secretary Ruth Kelly today threatened to strip First Great Western of its rail franchise if services did not improve.
As MPs voiced their anger over the performance of the rail company, which runs services through Oxfordshire, Ms Kelly urged managers to "get a grip".
She said the firm was being put "on notice" to improve services, which had been "unacceptable for far too long".
At Common's question time, Ms Kelly said the company had recorded the highest level of passenger dissatisfaction in a survey last autumn.
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