East Sussex Fire and Rescue confirmed the incident was “not expected to recur” but said they were still trying to identify the cause of the cloud.A spokesman for Sussex Police said neither the source or the nature of the gas cloud had still not been identified but said reports that it may have originated in France were “very unlikely”.He said: “Neither the gas nor its source have been established, but agencies are continuing to investigate and have not ruled out either onshore or offshore locations, although it does appear that it did sweep in from the sea driven by onshore breezes. Other suggestions have included an industrial accident along the coast, a contaminated shipping tanker washing ashore, or even the build-up of harmful algae.Dr Simon Boxall, of the National Oceanography Centre in Southampton, said: “If the reports from the public are to be relied on, it is weird that the “cloud” rolled in from the West. This is against the very light winds which should have driven in from the east. This implies a water borne cause. “The conditions yesterday were ideal for the development of a toxic algal bloom – very calm, high light levels, and a period of moderate runoff inputting high levels of nutrients into the sea for the preceding weeks.” Visitors to Birling Gap complained of vomiting, stinging eyes and sore throatsCredit:Twitter @Kyle_Crickmore He said US studies had shown cases where toxins from harmful algae can form clouds and drift ashore. “However, weather models suggest that an onshore source in northern France is very unlikely.”Police said the gas cloud had now dissipated and advice to keep windows and doors closed had been withdrawn. Around 150 people were treated at Eastbourne hospital after the mist past over Credit: EDDIE MITCHELL Beachy Head Lighthouse surrounded by mist on Sunday afternoon when the haze came ashoreCredit:SOCIAL MEDIA Henry Prout of Newhaven RNLI said: “The gas could have come from a container dropped at sea many, many years ago whose seal has finally broken or it could have come from a vessel doing a chemical clean, which is prohibited in maritime law.“Whatever the cause it is going to be extremely difficult to identify the source.” An algal bloom in The Channel may have been behind the mystery noxious haze that drifted ashore and left around 150 people needing hospital treatment, it has been suggested.Police and scientists are still trying to identify the source of the mystery gas cloud that left people with vomiting, stinging eyes and sore throats when it came ashore on the Sussex coast at Birling Gap, near Beachy Head.Emergency services at first pointed to a possible industrial leak in northern France, but then said wind patterns showed the cloud came from The Channel or further along the English coast. He said: “These cause respiratory problems and irritation, particularly in those with Asthma. It’s a long shot but the evidence points in that direction.”One scientist, who declined to be named, said: “The only possibility I can think of is that it might be a container of chemicals washed off a ship and ruptured. It might not necessarily be chlorine as there are other chemicals which produce a similar smell and reaction when mixed with water.” Want the best of The Telegraph direct to your email and WhatsApp? Sign up to our free twice-daily Front Page newsletter and new audio briefings.