Islamic State terrorists could launch a chlorine gas attack on Britain - a weapon used to kill thousands of British troops in the First World War trenches, an expert said today. Colonel Hamish de Bretton-Gordon believes that every British ISIS fighter will have been given chemical weapons training in the hope they will come back to launch an attack. The retired head of chemical and biological weapons for the Army believes the Tube or sporting events could be the target. Scotland Yard said that last year five Britons a week were heading to Syria and an estimated 500 of them may have returned to Britain. Fears: Colonel Hamish de Bretton-Gordon, left and right in 2007, recently retired head of chemical and biological weapons for the Army, is worried that ISIS might launch a chlorine attack in Britain . Colonel de Bretton-Gordon, who is now managing director of Avon Protection, believes that ISIS terrorists returning to the UK are 'highly likely' to use the gas, because it is easier to get hold of than weapons like guns and explosives. He has spoken out to warn the public what to do if there is an attack on UK soil and believes that it would be 'very survivable and a lot less dangerous than bombs and bullets'. He told MailOnline: 'I am convinced that IS fighters are all being given training in chemical weapons and the British ones, who are likely to be more educated, will all be targeted in the hope they may return home. 'They will have a reasonable idea on how to use chlorine and other toxic chemicals as a terror weapon. 'This could happen on a train or tube or even at a big football match. Acquiring weapons and ammunition is very difficult in the UK but you can get up to 90 tonnes of chlorine without any licence. 'The authorities must keep a close eye on those fighters returning to the UK, especially if they have a background in chemistry, and in particular anybody buying toxic chemicals'. Chlorine was used 100 years ago during the 2nd Battle of Ypres in April 1915, where the gas was vapourised into a cloud. It is classified as a 'choking agent', burning the lungs when inhaled in large quantities. But it is nowhere near as dangerous as nerve gases like sarin. Mr de Bretton-Gordon says that chlorine is being used on an 'industrial scale' in Syria and Iraq but that taking simple steps would help people survive an attack. Chlorine is readily available in Britain, used in swimming pools and decontamination in industry. 'My working with UK charity Syria Relief has focused in Syria on giving civilians the basic know-how to avoid chlorine. The same advice applies to Britain,' he said . 'Chlorine is not very toxic and the green and yellow clouds are easy to see and avoid. It is very non-persistent only lasting for a few minutes. It was used in the First World War but dropped because it did not work very well. 'It is key that ISIS don’t get the advantage of an unexpected chemical attack in the UK. If you can hold your breath for 30 seconds and run in the opposite direction you will be okay. If outside you should aim to climb or reach higher ground. 'Also urinating on a cloth and holding it to your mouth will help because urine kills chlorine. 'I train people in Syria to be aware of which way the wind is blowing because chlorine can travel quickly on the wind, but it also means you can avoid it. 'If the attack was on the Tube, chlorine is heavier than air, so it would quickly drop to the tracks. It is the panic that would create the carnage, so it is important people are prepared for it. 'Chlorine attacks are very survivable and a lot less dangerous than bombs and bullets, if you use simple procedures. ‘Fear of toxic chemicals and chemical weapons is the killer not the toxicity of the agents. ‘It is 20 years since the sarin attack on the Tokyo underground, but it took three years and $10m dollars to create 1kg of sarin and I think it is highly unlikely that ISIS or anyone else has the capability to do that in Britain'. Evidence: A gas canister lies at the site of a bomb attack on a road between Mosul, Iraq, and the Syrian border in northern Iraq, believed to have been used by ISIS . Target: Experts fear that the Tube or other packed areas may be subject to attacks by ISIS militants in the UK . Crude roadside bombs filled with toxic chlorine gas are now being used by Islamic State terrorists, it has been claimed. Iraqi officials say government forces have defused dozens of the devices in the course of their war with the fanatics and have produced video footage which backs up their claim. Mr de Bretton-Gordon said: 'Islamic State are all over these chemical weapons. The big prize is Mosul, its capital in Iraq. Lose it and they lose the country and have to retreat to Syria. 'I believe they will do anything to hold Mosul, and this will include chemical weapons use'. One bomb disposal expert said that the use of the chemical is a sign of desperation as the Iraqi Army makes advances against IS in Saddam Hussein's home town of Tikrit. Haider Taher told the BBC: 'They're resorting to this new method, putting chlorine in these home-made roadside bombs, which is toxic to those that inhale it.' He described how his team detonated a bomb in Tikrit that, unbeknown to them, contained chlorine. They immediately began feeling the effects of the chemical, experiencing 'painful choking' and blocked throats. Jennifer Cole, Senior Research Fellow at defence think-tank Royal United Services Institute, told MailOnline that although chlorine can be lethal, it does appear that it's being used to spread fear by IS. She said: 'Chlorine is easily available from a number of industrial sources and is very hazardous – causing breathing difficulties in particular and in extreme cases prolonged exposure can kill. 'Used in roadside bombs such as this, in the open air, it disperses reasonably quickly and so appears to be intended to cause panic rather than serious harm.' Terror: Chlorine was first used in the First World War and because it is heavier than air the clouds of killer gas would drop into trenches and wipe out troops . Chlorine was used by the British in the First World War, but it proved to be unreliable. In one attack in 1915 the gas blew back into British trenches after canisters of the chemical were fired from heavy guns at the Germans. In Tikrit, Iraqi soldiers and militiamen have reportedly retaken areas and key sites in the north, south and west, including a police headquarters and a hospital. Some 23,000 personnel are believed to be involved in the operation, the biggest offensive against IS mounted by the government since the jihadist group captured large parts of the country last June. The U.N. Security Council recently approved a United States-drafted resolution that condemns the use of toxic chemicals such as chlorine in Syria, while threatening militarily enforced action in the case of further violations. Chlorine, a chemical used in industry and water purification process, was first introduced as a chemical weapon at Ypres in World War I with disastrous effects because gas masks were not easily available at the time. In 1915, at Ypres, Belgium, Germany opened thousands of canisters of chlorine upwind of Allied troops, condemning many to an agonising death. Jack Dorgan, of the Northumberland Fusiliers, was hurt in a 1915 gas attack and said: 'Our eyes were streaming with water and with pain. Luckily again for me I was one of those who could still see. But we had no protection, no gas masks or anything of that kind'. British private Harry Cox said: They gassed us. And how I got out of it, I went up a tree. All the others they all went down in the shallow in the trenches of course there they all laid out all sprawled out and suffering agonies. Actually the battalion was wiped out – there was only five really fit men left'. By 1918 chemical weapons had proliferated on both sides – including phosgene, cyanide and mustard gas. Horrified by the effects, 15 countries signed the Geneva Protocol. More severely affected individuals may suffer acute lung injury (ALI) and/or acute respiratory distress syndrome (ARDS) and one in 100 will die. In October, Iraqi officials said Islamic State (IS) militants used chlorine gas during fighting with security forces and Shiite militiamen in September north of Baghdad. In the attacks, about 40 troops and Shiite militiamen were slightly affected by the chlorine and showed symptoms consistent with chlorine poisoning, such as difficulty in breathing and coughing,. The troops were treated in hospital and quickly recovered.
Expert fear IS terrorists will target the Tube or sporting events in Britain . Colonel Hamish de Bretton-Gordon believes Chlorine use 'highly likely'
He believes that every British ISIS fighter is chemical weapons trained . Chlorine gas would be easier to get because of its uses in industry . But Mr de Bretton-Gordon says that simple steps can help avoid death . Gas cloud covers small area so holding breath and running away will help .