The council need this area of land, which is not actually within the park, with its neatly cropped lawns, flowerbeds and trees to make room for the road to sweep down from the railway bridge.
It is now clear that the battle between the council and the protesting groups will be fought on two fronts.
Originally, the final decision was to be taken at the council meeting on April 25.
Now it seems there could be legal battle as well as the council debate.
The protesters have engaged Dawson & Co, solicitors, of Lincoln's Inn, London to consider an application for a judicial review "or other action."
Dawson & Co informed Southend Council last week that they had been instructed by residents campaigning as Priory Park Preservation Society against the proposals to dual carriageway Priory Crescent.
Their letter said: "It appears to us that legal proceedings are in contemplation in particular for a judicial review."
The protesters have singled out the open land on the opposite side to Priory Park in Priory Crescent as the main target for objection, arguing that it was part of the parcel of land handed over to the council to be kept as open space.
Dawson & Co maintain that in 1929 there was an agreement between Southend-on-Sea Estates Company Limited and the council for the land in Priory Crescent, along with Priory Park, to be transferred to the council which would maintain it.
They are arguing that both areas of land are subject to the same conditions.
Under the Open Spaces Act 1906, therefore, they argue that "the council shall hold and administer the open space in trust to allow and with a view to the enjoyment of the public as an open space."
The law firm go on: "Your council seems to have given no thought to the statutory trust nor do we see that your council is free to ignore that trust and simply say that the public no longer requires some of this land to be held upon that trust rather than some other purposes of the council."
It is also argued that even if the council uses the land for highway purposes the public is entitled to compensation for the loss of their rights.
THey also point out that while they appreciate the council has to weigh up competing public interests including the need to improve the road network they must give the residents the opportunity of a full hearing "on matters affecting their civil rights - article 6 of the Human RIghts Convention.
A report to the last meeting of the SOuthend Council Cabinet said that the status of the amenity land on the opposite of the road to Priory park was considered in detail in 1989 when the Charity Commission was supplied with copies of each of the cour conveyances forming the title of the park.
The Commission expressed the opinion that the amenity land was held for the purposes of open spaces and is not held on the charitable trusts of Priory Park.
The report went on: "The amenity land is the subject of a covenant with the Southend-on-Sea Estates COmpany for maintenance as open space. The company was acquired by Higgs and Hill, now Swan Hill, and negotiations will need to be concluded with the company for any road widening strip within this area.
"In summary, it can be concluded that the highway alignment does not involve taking land from Priory Park."
Town clerk George Krawiec said this is the advice we have been given by the Charity Commission and this is what we are acting on."
If it is then felt justified, a full hearing takes place before a High Court judge - which can be a very costly business.
The loser then faces the prospect of having to pay the full costs of the Judicial Review which will run into thousands of pounds.