Cornish walls which collapsed just a few weeks after being built as part of a £330million dualling scheme on the A30 were not properly constructed, National Highways has admitted.
Three kilometres of Cornish hedges have already been built along the newly-reopened A3075, but large sections between the Chiverton Cross roundabout and the first Perranporth turn-off have fallen apart.
Many people, including professional Cornish hedgers, have criticised National Highways' contractors for not using the traditional technique for the build.
If well-built, they can last hundreds of years and some in west Penwith are believed to be 1,500 years old.
The work was part of a major infrastructure project and contractor Costain was brought in to build eight miles of traditional Cornish hedges alongside the new route near Truro. They will be restoring existing ones too.
Earlier this year Costain said the Cornish hedges were being built following guidelines set out in the Guild of Cornish Hedgers’ bible, 'Building Hedges in Cornwall'.
However National Highways has now admitted the Cornish hedges along the A3075 Newquay Road were not done properly.
They said they did not follow the 'design guidelines' which is why they have collapsed or are on the verge of collapsing after the first month of winter rain.