Remarks: "Water Dreaming" (Del 5/90) on Twy Alpha prior to departure off Rwy 34L as BA016 to Singapore and London with 270 passengers on board. The crew declared a "Mayday" just after take off with a fire reported in the forward cargo hold and made an emergency overweight landing on Rwy 34L about 20 minutes later. There were no injuries and only minor damage to the jet. The ATSB report into the incident identified the forward galley chiller boost fan as the cause of the small and localised fire.