Originally Posted by
treadigraph
Just reading elsewhere that it was a Spitfire V from Biggin (not the Kent Spitfire IX); the display was described as beautiful by another onlooker in the vicinity.
Now, can I slip out of work for a two hour lunch on the 18th and watch all those Spitfires depart Biggin...? 
So, as the OP said, definitely not a Merlin engine then
G