Network Rail signed up to "highly ambitious" targets which "proved too optimistic", according to the Rail Delivery Group.
Michael Roberts, the director general of the group, which represents operators, said: "Britain’s railway is carrying record numbers of passengers and freight and in some places is virtually full to capacity, making continued investment crucial."
He added: "The majority of proposed enhancements will still go ahead, and it is important that the industry, government and regulator learn from this situation to ensure we do better in delivering the future improvements the railway needs.”
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