By Dan Warburton Reckless sellers are offering to deliver bottles of potentially fatal laughing gas within 20 minutes. We discovered the callous trade after an inquest heard how Ellen Mercer, 24, perished following nitrous oxide binges. Student Ellen had abused 600g bottles, equivalent to 75 of the usual 8g canisters, after ordering them online. Ellen’s death was related to “long-term complications of nitrous oxide use,” the coroner said at her inquest. Ellen, 24, told her boyfriend not to call an ambulance as it “kills her buzz” when she began suffering leg and back pain. She was left unable…