What was that? :: 4/3/14

So I'm sat in my living room, just after noon, and hear the sound of an aircraft approaching overhead. Not the usual signature roar of a Merlin or other recognisable warbirdy piston, so no rush out the door to catch a glimpse.
So imagine my disappointment when I did finally get off my arse and look outside, to catch a sight of what I assume was a silver Spitfire at a fairly low level.

The dog and neighbours were probably wondering why I was shouting about oar fixings…

Was it SM845?...