They are angry because they say that nothing has been done to solve the problem despite their protestations over the past three years.
One shopkeeper in East Street says the stench was so bad last week that shoppers were walking along the road with handkerchiefs across their faces.
John Cox, of Trelfers Jewellers, said on Friday: “This morning it would have been more pleasant to have stuck our heads into a cesspit than breathe the air in East Street.
“You would be joking that you needed a clothes peg for your nose if you entered a toilet cubicle smelling like this - the smell is that intense.
“This has been going on for far too long - in excess of three years - and is not acceptable.”
Fellow trader Vince Cassar, of nearby Town and Country Weigh, said: “At the moment it is bad. Then it clears and then it comes back really bad again.
“I’ve seen people with handkerchiefs on their noses. It’s ridiculous.”
He said that the foul stench was putting off shoppers from visiting the area.
“We’re losing business,” he said, “people come here and say ‘what is this stink?’ This has been going on for too long.”
A spokesman for Horsham District Council said: “The council continues to work in conjunction with the Highways team at West Sussex County Council to rectify this issue. It is now for the highways team to get back to us on what plans they have in place to resolve the problem.”
A spokesman for the county council said that highways workers had “previously jetted and cleaned the surface water drainage system in East Street, but this did not resolve this intermittent problem.
“We are continuing to try to identify what may be causing the smell so that the appropriate solution can be actioned.”