The toll on the bridge was due to rise in October

Donald McGougan, treasurer of the Forth Estuary Transport Authority, said the bridge's running costs would be unaffordable without the 20p rise.

The hearing in North Queensferry was triggered by a single complaint.

George Campbell, from Glenrothes, claimed bridge tolls already generate millions of pounds a year.

FETA wants to increase the toll for cars to �1, the first rise since 1986, to meet operating and maintenance costs over the next 14 years.

Mr McGougan, outlining the authority's case, told the inquiry: "If there is no increase in tolls it is estimated that the management, maintenance and operation of the Forth Road Bridge would not be affordable and would result in an estimated debt of �29.17m by 2018.

"In my view, the proposed revised tolls are reasonable and are no higher than they need be in order to meet projected liabilities and provide an adequate reserve against risks facing the authority."

'Arrogant' assumption

Feta expects to spend more than �9m this year on bridge maintenance, but that figure is likely to rise to �14.4m in the next five years, Mr McGougan added.

Under questioning from the Reporter, Malcolm Mahoney, he pointed out that the tolls would be �1.56 if they had risen with inflation since 1986.

He added that holding the public inquiry and the delay to the new toll regime, which was due to be introduced in October this year, would cost FETA �1.1m in lost revenue.

Tom Minogue of Fifers Against Tolls Increase asked why FETA had not included the cost of the inquiry, which is being held at the Corus Hotel in North Queensferry, in their contingency plans.

He said: "I just thought it was at best negligent and at worse arrogant to assume there would be no public inquiry."

Mr McGougan said the expense would be absorbed by reserves earmarked for unexpected capital works.

It is expected FETA will introduce a road user charging scheme in 2006, but Mr McGougan said the toll increase is necessary in the interim.