Council leaders have reiterated their call for energy bosses to rethink plans to build pylons across swathes of countryside - even though a report concluded the scheme is the cheapest option.
They say that the report also highlighted how there should be no need to rush into a decision and a delay by a few years could make an offshore solution more affordable.
National Grid's plans for a 112-mile line of 50-metre high pylons, from Dunston, near Norwich, to Tilbury on the Thames estuary, have sparked widespread opposition.
Bosses say onshore pylons are needed to take energy from wind farms off the Norfolk coast to the southeast of the country.
But critics claim National Grid has been too quick to rule out an offshore solution, with undersea cables taking the power to the Thames estuary.
READ MORE: Proposed Norfolk pylon route revealed by National Grid
Norfolk, Suffolk and Essex county councils have joined forces to oppose the plans and commissioned Hiorns Smart Energy Networks to carry out an independent review.
That review concluded the unpopular overhead lines and pylons are the most economical option, which has been National Grid's assertion.
The report said the onshore approach could cost up to £2.02bn, while an offshore scheme could cost £4.44bn.
But, the report also challenged National Grid's stated date of 2030 for the project to be in place, and suggested the need for additional transmission capacity would be closer to 2035, or beyond.
Council leaders say that shows there is still time for the offshore model to be developed and to bring down its costs, rather than putting pylons across fields and close to communities.
Kay Mason Billig, leader of Conservative-controlled Norfolk County Council, said: "We can see that the need for this capacity by 2030 has been overstated by up to five years.
"I would urge the government to use this extra time not to rush ahead with building pylons years before they’re needed, but rather to thoroughly test and cost-up the alternative options that could, if implemented, significantly reduce the impact on our communities and precious environment."
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