According to a High Court judgement, River Farm, in Tillington, West Sussex, has become home to 21 caravans lived in by workers employed in the viticulture industry.
Landowner David Langmead was in 2005 granted planning permission by Chichester District Council to lay down an agricultural hard-standing, a new access track and an earth bund at the site.
But that was subject to tight conditions that caravans on the site should only be lived in by agricultural workers employed on River Farm, the court heard.
The council also said they had to be removed immediately at the end of the viticulture season, between March 1 and October 31 each year.
In 2009, Langmead was granted temporary consent to use the caravans to accommodate seasonal workers employed in agriculture locally.
That expired in 2014 but, since then, the caravans have been permanently stationed on the site, said the judge.
And they have been used throughout the year to accommodate workers "employed in viticulture in various places in southern England".
In November 2016, the council issued an enforcement notice demanding removal of all caravans from the site, other than those occupied by agricultural workers employed on River Farm.
Following a public inquiry, that decision was upheld by a planning inspector in September last year.
The inspector said that there was "no evidence that any of the people who occupy the caravans work at River Farm".
"Year round occupation by workers working elsewhere has resulted in what is in effect a permanent residential caravan site," the inspector said.
The caravans created a "significant urban element" that effected the "tranquillity and character of the national park", he added.
Although their presence only had a "very slight level of visual effect" on the local landscape, the inspector upheld the enforcement notice.
Challenging that decision, Langmead pointed out that many vineyards rely on the workers who call the caravans home.
He argued the inspector had ignored his proposed mitigation measures, including erection of fencing and hedge and tree planting around the site.
Dismissing his appeal, however, Mr Justice Lane could find no flaw in the inspector's conclusions.
The inspector had been right to say that, even if the enforcement notice were overturned, the seasonal condition would still apply and the site would still have to be cleared of caravans twice a year.
And the proposed mitigation measures were not relevant to the issue of whether the caravans could be occupied by workers not employed on River Farm.
Langmead v Secretary of State for Housing, Communities and Local Government. Case Number: CO/4614/2017