From
http://www.rafmuseum.org.uk/mileston...ivil/1967.html :
4 July (1967)
The United Kingdom government begins sonic boom tests over the country, using Royal Air Force English Electric Lightnings to produce random booms.
The one sonic boom that will stuck in my memory was produced by a Mig, flying low over the city in 1991. An unexpected loud explosion sound, not nice.