Protesters say the breakwater is in danger of collapsing into the sea

The professor of civil engineering, who sat on the panel to assess the breakwater's future, said economic arguments favouring the current plan were never satisfactorily made.

Professor Chris Flemming was part of the panel whose report was published in 1998.

It was commissioned the previous year by the joint consultative committee.

Serious breach

Professor Flemming said the argument that a second smaller breakwater would be cheaper in the long run was based on there being a serious breach to the structure within the next three to five years.

But he said that had not been the case.

He said: "There were a number of ideas investigated using physical models to try and devise a scheme to preserve the old breakwater.

"It was decided there was a need to build a fairly massive structure on the front of the old breakwater at an extremely high cost.

Increased cost

"The cost was increased by the fact it was assumed the construction would have to stop during the winter periods.

"It was therefore concluded that it would be cheaper to build a new, smaller breakwater inside the old breakwater."

He said the panel also found fault in other economic arguments in the plan currently favoured by the Guernsey authorities.