Typhoon jets caused a "loud bang" in the early hours of Sunday (Picture: MOD).
Two Typhoon jets caused a sonic boom in the early hours of Sunday, when they were scrambled to an aircraft which had lost communications.
The RAF said the fighter planes were deployed from RAF Coningsby in Lincolnshire shortly before 04:10am.
The aircraft were the cause of an explosion-like sound which was heard across swathes of the south-east, with Hertfordshire Fire and Rescue receiving a "large number" of calls.
People living in Essex, west London and Stevenage were among those tweeting to say they had been woken up by the noise.
"Two Typhoon fighter aircraft from RAF Coningsby were scrambled at 04:09 this morning, as part of the UK's Quick Reaction Alert procedures, after an aircraft lost communications in UK airspace," said an RAF spokesperson.
"The aircraft was intercepted and its communications were subsequently re-established. The Typhoons are returning to their base."