Why 9 planes had to declare an emergency above one of Europe's busiest airports

Nine planes declared emergencies over London after Gatwick temporarily closed a runway overnight, forcing 14 flights to divert.
The disruption followed a technical issue with a British Airways A320 that stopped on the runway; the jet landed safely and passengers disembarked normally.
Some aircraft diverted as far as Bristol and Birmingham, and one easyJet flight left passengers stuck onboard for over two hours at Stansted while waiting for refuelling and ground crews.