Valley Grown Nurseries in Harlow, Essex, is due to complete the 92,000 sqm block of glass for peppers this month ready for an official opening in January by the Princess Royal.
Lea Valley Growers Association (LVGA) secretary Lee Stiles said the opening marked the second phase of a glasshouse expansion that started five years ago with the first planning application.
"It was the basis of an unsuccessful judicial review from the Lea Valley regional park authority, which has now conceded the National Planning Policy Framework (NPPF) allows for such buildings even in the park.
"We hope the battle is over, but the park authority may lobby the government to change the NPPF, which it is entitled to do.
"However, post Brexit we need to produce more food and doing it under glass is an ideal way of growing more fruit and vegetables on less land."
The battle came to a head last year when a consultation on a park development framework from the Lea Valley regional park authority included plans to squeeze out commercial horticulture expansion.
The authority's draft proposed to "resist significant expansion of existing glasshouse businesses or the location of new glasshouse businesses".
Stiles said this week: "Throughout all this uncertainty the growers carried on with the project quite bravely. The crux was the site was in the park area, even though the authority didn't own it."
He said the new glass was meant for tomatoes but delays caused by fighting the judicial review prompted bosses to go for a faster-return crop. It may eventually be used for tomatoes.
The new building had super-efficient ventilation and a white structure instead of the more usual bare metal to maximise light in the building.
LVGA also welcomed this week the Epping Forest District Council local plan, which Stiles said was "supportive" towards the glasshouse industry.
"This is the council's plan for the next 20 years and though there are a few tweaks we'd like to make, its vision is supportive of the expansion of our sector."
According to a statement this week from LVGA on the council's draft plan the association welcomed the council’s statement to "to support the diversification of the agricultural economy, including the expansion of the glasshouse horticulture industry, subject to appropriate environmental considerations".
Established in 1911, today the Lea Valley Growers Association represents over 100 members and 95% of protected horticultural growers in the Lea Valley.
The area is the UK’s largest cucumber and sweet pepper producers accounting for over 200 million pieces per annum. Local horticultural generates £500m and employs around 2,500 jobs annually.