A consortium including Shell WindEnergy is planning 270 turbines for an offshore site between Kent and Essex.

Shell spokesman Andrew Murfin said the development could not go ahead until objections raised by the Port of London Authority (PLA) were addressed.

"We are continuing to talk to them to try to resolve those issues," he said.

We are aware that they have some ongoing concerns about a particular part of the site towards the south Andrew Murfin

A planning application for the wind farm was submitted this week by London Array Ltd, which includes EON UK Renewables and CORE Ltd as well as Shell.

The �1.5bn development would cover 152 sq miles (245 sq km).

The PLA has been conducting trials at a smaller wind farm being built near Herne Bay.

"The trials indicated that these structures can have a detrimental effect on ships' radar," said Roy Stanbrook, harbourmaster at Gravesend.

"It can make it difficult for one ship to detect another.

"This is caused by the presence of secondary echoes which mask areas of the radar screen."

He said the PLA was in uncharted territory as there was "precious little" data available from other wind farms.

"We are the area which seems to have been conducting trials with turbines close to main shipping channels."

'Ongoing concerns'

Mr Murfin, Shell's vice-president for development, said the consortium had been discussing the project with stakeholders, including the PLA and the Maritime and Coastguard Agency, for two years.

"We are aware that they have some ongoing concerns about a particular part of the site towards the south," he said.

The wind farm would be 20km (12.4 miles) out to sea and Mr Murfin said it would not be visible from the shore except on very clear days.

There would also be an electricity substation at Graveney, off the North Kent coast.