Plans to revamp a harbour, creating hundreds of jobs, have been plunged into doubt after council officers decided they were unworkable.

Brighton and Hove City Council yesterday said potential costs of almost £200 million made it impossible to go ahead with regeneration proposals for Shoreham Harbour.

Planners want to tear up the Shoreham Maritime vision drawn up five years ago and start again.

The long-term proposals included an enterprise park on the north canal bank, creating at least 500 jobs.

As well as new industrial units, it was also hoped to provide leisure facilities, a restaurant, pedestrian walkways and landscaping.

But a study, published yesterday, found the necessary transport improvements would come at too high a price.

Existing roads are believed to be unable to cope with the extra traffic that would be created by any significant development.

Officers investigated the two most likely options but found a tunnel would leave them needing to raise £177.5 million.

They also found they would be £92.5 million short if they decided to build a new surface road linking the harbour with the A27. These figures include the costs of reclaiming land.

Brighton and Hove said it was unable to meet these costs, even with help from project partners West Sussex County Council and the South East England Regional Development Authority (Seeda).

Shoreham Port Authority, which planned to finance the £5 million enterprise village, has refused to help with the cost of transport improvements.

City council leader Ken Bodfish said: "We have fully considered the options. There is a significant funding gap which cannot be met by the public purse or the private sector without changes to the existing vision.

"The proposed surface road would affect, or result in the demolition of, up to 87 homes. It would potentially increase noise pollution and reduce air quality in the area. This is not an option.

"We're going to have to knuckle down and find a deliverable vision for the future but it must work economically and politically."

Local transport measures, which were considered but rejected on grounds including poor accessibility, high costs and potential disturbance, included:

Surface level and tunnel routes running along the line of the Adur and Brighton and Hove boundaries
Routes in a corridor between Church Road and Boundary Road
Extension of a tunnel beyond the Hangleton Link to the A27
Direct tunnels to link to the south side of the port area.

Rod Johnstone, chief executive of the port authority, said finding the funds was for the local authorities and the Government.

He said: "The deliverability of the transport measures is a political issue and certainly not one for the port authority.

"Our remit is to develop the port and its economic impact on the area and that will continue.

"It's business as normal for us as far as funding is concerned. But this is obviously a setback for the deliverability of the vision itself in the longer-term.

"We'll now wait for the various authorities, Seeda and the Government to come up with a sort of 'Son of Shoreham Maritime'."

Brighton and Hove City Council opposition leader Brian Oxley said: "Shoreham Maritime provides a unique opportunity to secure additional homes, jobs and commercial development land.

"But if it is to meet the future need we'll have to bring many more ideas to the table."

Adur District Council was taken by surprise by Brighton and Hove's announcement and officers last night wanted to examine the 32-page report before responding. Planning officers are due to make their own report to district councillors on Thursday.

Marine ward councillor Liza McKinney, of Shoreham Beach Residents' Association, said: "We know that without improvements to the A27 or the A259 we'd end up with gridlock.

"This was always going to be a long-term, phased proposal and we never dreamt the money was going to fall from the sky."