Allotment owners, who have been told their plots may be built on as part of the Watford Health Campus, have demanded to know exactly why the previously protected area is now under threat.
Members of West Watford and Oxhey Garden Society have said they will lose years of labour if their Terrace Farm plots are concreted over as part of the £1bn project.
Tenants on the site, behind the Vicarage Road stadium, have been informed in the past few weeks that it could now be included in the Health Campus as developers bid for the contract.
The scheme aims to redevelop the land around Watford General with a new hospital, housing and leisure facilities The original Health Campus masterplan, drawn up in 2007, showed the development built around the Terrace Farm allotments, which have been in use since 1896.
Mary Reid, a former chairman of the society, said the allotment holders needed more solid evidence about why Farm Terrace land had now become crucial to the Health Campus.
She said: "We were led to believe in 2007, when we finally got to the stage of outline planning, that there would be a masterplan keeping the allotments.
"This was a bolt out of the blue, which is why the allotment tenants are so upset. We know officially we will be consulted, but we can read between the lines.
"We are one of the elements of the Health Campus and we have not been given the full information about whatever it is that has changed which means the allotment land needs to be considered.
"We need proper plans and a proper explanation."
At a council meeting on Monday, Watford’s elected mayor, Dorothy Thornhill, said the situation had changed due to the worsening economic climate and the extra land may be needed to make the project viable for developers.
On Monday, Watford Borough Council’s Liberal Democrat ruling cabinet voted to look at using all, half or none of the Farm Terrace land as part of the Health Campus.
After the meeting, the mayor’s office released more detailed reasons why the land may now need to be used in the development. These included the land being used for hospital buildings, being given to developers to recoup the mounting costs of the project, use for a new school or to give the campus a more spacious layout.
However Gerry Barker, chairman of West Watford and Oxhey Garden Society, said if the allotments were lost, tenants would lose years of hard work.
He said: "If you move the allotments and give someone an alternative site, it will take three years to get a response. Some people have very well established plants and trees. It is irreversible in that respect."
The allotment holders have been asked to form an official group to consult with developers and the council over the Health Campus.
Watford’s opposition Labour group said any consultation with allotment holders should take their views seriously and not be a "talking shop".
Nigel Bell, leader of the Labour group, also disputed the idea that the Health Campus could not be viable without using the allotments.
He added: "It should not be implied that any questioning of why the allotments should be given to the developer is in any way a lack of support for the health campus."