Apparently two fighter jets were scrambled from Lincolnshire to intercept an "unresponsive" plane flying over southeast England. They were allowed to fly at supersonic speed, and thousands of people heard a sonic boom at around 4:20am.
It appears the plane was a passenger jet flying from Israel to the USA, but developed radio problems over Germany. It was not carrying passengers but was being flown from a seller to a buyer of the aeroplane.
The pilot "nearly had a heart attack" when he saw the fighters.
It looks like I was nearly at the centre of the boom, but I didn't hear a thing.
It does show the level of concern about terrorism and a possible second 9/11 attack.