Hercules at Marshalls.

For the second time this week i have just been watching from my house in Duxford a Hercules being thrown around the sky at or near Marshalls Cambridge Airport. Its taken up almost to the vertical to what seems the point of stall before being pushed over the top into a near vertical dive and pull around. And all at what seems a relatively low altitude.
I presume its on an air test of some sort, but just wondered if anyone else had witnessed it?