Local people joined councillors and Hayes and Harlington MP John McDonnell on Saturday morning, as they marched from the Hayes town bandstand in Station Road, Hayes, to the construction site at Botwell Common, off Botwell Lane.
People chanted and carried banners, one of which read "I can't walk my dog in Lidl" - a reference to the council selling off the former Hayes Swimming Pool site in Central Avenue, a brownfield site campaigners had urged the borough to use for a new school, to Lidl.
The discount supermarket chain is preparing plans for a new store.
Addressing the crowds, Mr McDonnell outlines concerns that the rest of the park, green belt land, would be turned over for a secondary school.
He added: "We have to keep slugging it out with them (the council) to try and prevent this development going any further, but also to demonstrate to them that we will not allow them to take the rest of the park. We'll continue to pursue whatever legal actions we can and maintain the pressure on the council."
Campaigners allege that the council did not undertake an equality impact assessment when drawing up its plans for the school.
Mr McDonnell, with the Friends of Lake Farm and Labour councillors in Hayes wards have taken legal advice from Irwin Mitchell solicitors, and been advised that they have grounds to challenge the council's decision to proceed with the project. Irwin Mitchell confirmed their involvement, but cannot comment further.
The new school will accommodate 635 pupils, to help meet a projected growth in pupil numbers in the borough in the coming years, and the council has repeatedly outlined a commitment to meeting the future needs of children in Hillingdon borough when answering critics.
Article by Jack Griffith at GetWestLondon.co.uk
Photos by Tony James