Protesters turned out in force to descend on Westbury's Lafarge cement works on Saturday as they opposed plans to burn waste materials as fuel.

Meeting in the Market Place at 2pm, hundreds of marchers surged through Westbury town centre before heading up to the main gates on Coach Road. Police had to stop a small group of protesters entering the plant, but otherwise the march passed off peacefully.

Lafarge has applied to burn recycled liquid fuel (RLF) for a six-month trial period, but protesters fear the plan does not properly address their health concerns. The Environment Agency was due to give its verdict on the application today, but on Tuesday announced it was putting it back until June 11.

Organiser Richard Baxter, from the Air That We Breathe pressure group, was delighted with Saturday's turnout, which he estimates at more than 500. He believes the march may have contributed to the Environment Agency's decision.

He said: "I think the police were taken aback by the passion of the walkers they had to call for reinforcements. I didn't really know how many would turn out, but this shows the strength of feeling on the issue.

"This was no unruly mob but a group of parents with their children and pushing toddlers in pushchairs, terrified for the future of those children. Ordinary people like this have taken to the streets in frustration because they feel that their fears and concerns are not being listened to."

Since it first announced plans to burn RLF in 2002, Lafarge has strenuously maintained that the fuel has environmental benefits and is not harmful. But campaigners say the firm has not produced evidence to support this view.

Mr Baxter said: "If this is such a fantastic fuel why aren't they shouting about it from the roof tops? They know as well as we do that there has been no long-term health study into the effects of burning either tyres or toxic waste."

Sgt Jim Stannard, of Westbury police, estimated Saturday's turnout at between 250 and 300.

He said: "A small group of activists broke away from the main group and started to move towards the cement works. But they were quickly halted and encouraged to return to the main body of the march."

West Wiltshire MP Andrew Murrison joined protesters on the march and fears Westbury may become home to a back door incinerator disposing of waste from across Europe.

Environment Agency spokes-man Colin Babb said: "The main reason for the extension is to allow time to resolve an emergency planning issue raised by West Wiltshire District Council and to finalise technical work relating to environmental monitoring."

Lafarge Cement UK's Westbury works manager John Collinson said the firm understood people's concerns but said the fuel had been used successfully elsewhere and it would be environmentally and commercially irresponsible not to pursue it.

He said: "Health and safety is our top priority at all times. We were extremely surprised last Saturday when the group, including local elected representatives, entered the factory grounds.

"Industrial operations like this have health and safety requirements for good reason; it is reckless and irresponsible for people to ignore such requirements, potentially putting their own health and safety, and that of our employees, at risk."