London:- British athletics great Christine Ohuruogu, who was crowned 2008 Olympic champion in the women's 400 metres, announced she is retiring on Saturday. She was handed a one-year ban for missing three out-of-competition drug tests in 2006 with a BOA bylaw dictating that any doping offences were punishable by lifetime Olympic bans. However, despite losing her case at the CAS, she found an unlikely saviour as the BOA allowed her appeal in Nov 2007. "Today is the start of the British Championships and, as I won't be there competing, I feel it is a good time to formally announce my retirement from competitive athletics," she said.