Concern grows that cause of toxic plume last month, which left 150 people seeking hospital treatment, may never be known

MPs have criticised a decision to wind down an investigation into the mysterious chemical haze that caused Sussex beaches to be evacuated and left dozens of people reporting sore eyes and breathing problems.

People affected by the incident expressed alarm that they may never know the cause of the toxic plume that gave them sore throats for weeks after it drifted on to Birling Gap and other beaches on 27 August.

The Maritime and Coastguard Agency (MCA), which was leading the investigation, had said it was exploring a range of possible causes including gas from shipwrecks and possible illegal emissions from 180 ships identified in the Channel that day.

But it has said it cannot continue the investigation because the type of gas involved was never identified and samples were not taken. The agency said: “If the identity of the gas becomes clear it may allow the MCA to re-establish a broader but better targeted ship-source search and the ability to determine whether or not any illegal action(s) have occurred.”

About 150 people sought hospital treatment after the incident. Speculation that the source was a factory in France, or an algae bloom, was quickly dismissed. The most likely source of the gas is still considered to be fumes from a ship in the Channel illegally flushing its tanks with chemicals.

Stephen Lloyd, the Liberal Democrat MP for Eastbourne, said the MCA’s decision to halt its investigation would encourage ships to continue polluting.

He told the Guardian: “If it is, as many suspect, a cargo ship cleaning one of its tanks illegally, they have got away with it. It is one of the biggest shipping lanes in the world and if one ship has got away with it, it is not the sort of message that is going to effectively deter others from doing the same.”

Lloyd said he was disappointed that there appeared to be no protocol in place to capture samples of gas in such incidents.

He said: “We are lucky that no one appears to have had any longstanding ill-effects from coming into contact with the haze across Eastbourne and beyond. But its impact was certainly significant enough for 150 to turn up at the Eastbourne accident and emergency department. To find at the end of all this that no sample was collected is deplorable.

“For the Maritime and Coastguard Agency on one the hand to tell me they were narrowing down a culprit from the 150 ships and then three weeks later say they can’t do that because they do not know the makeup of the haze is unacceptable.”

The Green party co-leader Caroline Lucas, some of whose Brighton constituents were affected by the gas, also expressed concern.

“People were rightly worried by the air pollution which swept in from the sea, and I had hoped that the MCA had been spending this time working out both the kind of toxin that was in the air and where it came from,” she said.

“If we’re going to avoid a repeat incident we need the full facts in front of us, which suggests to me that the winding down of this investigation could be both premature and risky.”

Laura Knight, a drama therapist from Brighton, was evacuated from Birling Gap beach along with her partner and two young children. “The reaction was very unpleasant so it must have been a very harsh chemical. I had a sore throat and a cough for a good two weeks afterwards,” she said.

Knight attributed the failure to identify the chemical to “ineptitude or conspiracy”. “The fact that they came on to the beach with gas masks and protective suits yet still didn’t appear to be able to test the very thick chemical air to find out what it was, I find concerning,” she said. “It is just bonkers not to be sending scientists to investigate as well as emergency services.”

Dan Sankey, whose trip to the beach was cut short when he felt his eyes burning, said the authorities should have done more to identify the source.

“I think the investigative response team could’ve done more in the first instance,” he said. “In the absence of fact I’ll continue to entertain all possibilities out there on the matter.”