I have encountered this warning lamp coming on about twice in 2 years. On both occasions its when I fill up at Tesco and within about 5 mins if I am stuck in traffic with my foot on footbrake and waiting on the traffic to move, ie not in Neutral.
The lamp actually went out itself in about 24 hours. Dirty fuel? Change of fuel from Shell to Tesco then burning rich or lean as a result? or just air in the system or something (out of my depth here obviously).