The insulation was burnt outside the retainer clip, but inside was still in good consition. The fuse also did not blow. So, can surmise that the possible cause of fire was over-tightening of the clip.
The power point was affixed on wooden panel and there was a cabinet beside. The fire quickly spread to these but fortunately, the sprinkler was directly overhead. Damage was limited.
Learning points:
1. Do not obstruct fire fighting equipment
2. Check plugs and conenctions regularly for any sign of overheating.