Matches the clues very well Jim.
It's grey in parts (most of it in fact!), it's a monoplane, and it's got two engines, and it is a Mosquito!
It's the Mosquito NFII of Tony Agar, who started the restoration in the early 1970s, with some small sections and a cockpit, and it now has both engines running, and is based at the Yorkshire Air Museum, Elvington.