Hear, hear is appropriate, treadigraph - it happened twice, about five minutes apart!
Heard both quite clearly in Lytham, near Blackpool, and didn't realise what it was. It sounded like a deep rumble for three or four seconds followed by a thud. Not what I would I expect to hear of a sonic boom (more like a double thud followed by engine noise). I thought my neighbour was dragging a heavy bit of furniture across a wooden floor and then dropping it. Couldn't think why he did it twice!
Still, as PB says, well done to the pilot. Nice to hear it being used in the manner intended!
GG