ONDON, Sept 22 (Reuters) - Britain warned its food producers on Wednesday to prepare for a 400% rise in carbon dioxide prices after paying tens of million of pounds to get CF Fertilisers (CF.N) to restart production in a deal that will last for three weeks. read more The deal buys Britain some time to secure suppliers from other sources as it seeks to prevent the shutdown on production of a wide range of food and drinks. WHY IS CARBON DIOXIDE IMPORTANT? The food and drink industry is the largest user of carbon dioxide with the gas used in a wide range of beverages including beer and soft drinks. In the meat sector, it is also used to stun animals prior to slaughter while bakers often use it in a packaging process which prolongs the life of products such as crumpets and cakes. The gas has many other applications outside of