The Beaminster Tunnel in Dorset is unlikely to be re-opened for several months.
It was closed earlier this month after a landslip that killed two people.
Engineers have found that the slope at both ends of the tunnel is extremely dangerous and liable to further collapses. Dorset County Council has brought in experts to find the best way forward.
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Hotter again on Monday with temperatures up to 25 degrees. Cooler on the coast and on the Isles of Scilly.
A clear night, hotter again on Monday.
Highs this afternoon of around 23 or 24 degrees. Cooler on the coast.