The decision by Royal Mail to abandon trains in favour of road transport was bitterly opposed by the Department of the Environment.
In a private letter to the leader of the rail network's biggest union, the Environment minister Lord Whitty registered his dismay over the move, declaring it was in contradiction to government policy.
He told the RMT union's general secretary, Bob Crow: "I personally, and this department also, have grave concerns about the Royal Mail decision, which seems to be heading in the opposite direction from the aim of a more balanced, environmentally friendly and integrated system."
The letter, dated 22 September but which only became public yesterday, went on to express regret that his department had no control over the decision.
He said the Government had given Royal Mail greater commercial freedom and so it would be inappropriate for ministers to intervene.
Royal Mail has come under pressure to rethink its decision, announced on 6 June, and is discussingways of continuing to use the rail network.