The Boeing 777 left Gatwick at 7.38pm on Tuesday night for what should have been a 12-hour, 6,050-mile flight south of the Equator.
The plane flew normally over France, Switzerland, Italy and the Mediterranean before entering Egyptian airspace and flying close to the Nile.
But at around midnight GMT, the aircraft turned around and flew back on almost exactly the same course. The airline later said it was “because of a technical issue”.
Rather than touching down at on the tropical Indian Ocean island of Mauritius on Wednesday morning, the passengers found themselves back at the West Sussex airport at 4.45am.
The flight has been rescheduled for 4pm on Wednesday. If it operates as expected, the passengers will finally reach their destination more than 20 hours late.
At the other end of the route, hundreds of passengers find themselves with an unexpected extra day in Mauritius.
They were told by email: “Despite our best efforts, we’ve made the difficult decision to delay your departure to London Gatwick overnight because of a technical issue with the outbound aircraft.
“We don’t underestimate the inconvenience this will cause. We’re really sorry for the change to your travel plans and we’ll do everything we can to help.
“Your new estimated departure time is now 10:05 local time on 8 December, arriving at 18:25 local time on 8 December.
“You are able to claim reasonable costs for hotel accommodation, local transportation and any essential items you may require overnight.
“We’ll also cover the cost of meals up to £20 per meal for adults and £10 for children under 12 years of age and up to £25 for telephone costs/internet access.”
The message makes no mention of the £520 in compensation that British Airways must pay to each passenger under European air passengers’ rights rules if they arrive three hours late or more due to a technical issue.
A spokesperson for BA said: “Our pilots decided to return to Gatwick as a precaution due to a minor technical issue, and the aircraft landed normally.
“We have apologised to our customers for the disruption to their journey and our teams have arranged a replacement aircraft to get everyone on their way as quickly as possible.”