Lamington Viaduct has suffered further structural damage from bad weather meaning that it will not reopen until the first week of March, 2016.
Alternative routes are in place along the West Coast mainline and they will add 1 hour extra travel time to journeys.
The viaduct has been closed since December when it was severely damaged by Storm Frank in December.
Residents in a Cumbrian village are angry that work to repair their flood-damaged bridge is moving too slowly.
The temporary bridge to replace Pooley Bridge, which was washed away in December's floods, should be in place by Easter.
It is estimated repairs to one of Cumbria's most popular walking and cycling paths between Keswick and Threlkeld could take up to two years.