I was on BA042 CPT-LHR (G-CIVD) last January when some 2hrs out of CPT the oxygen masks dropped. It was startling!
After 15 mins Captain popped up on PA announcing deployment had been a technical fault
I finished my cheese and port and we carried on our merry way to LHR.
This surprises me. I thought that if masks deployed, there was a requirement to land at the nearest suitable airfield. The reason being that even if the deployment was accidental, many PAX would have pulled the pins and activated the oxygen generators -- therefore if a real emergency developed another few hours into the flight, they wouldn't have any more oxygen available.