Thanks for the replies.
The lens and camera were in a cupboard London. I'm keeping them wrapped in a bag separate from the rest of my kit.
I've no idea how long this has been there, I've only just pulled the thing out of a cupboard a couple of weeks ago.
There doesn't appear to be any web/tentacle like structure (sounds like something out of Alien). It's more like opaque cloudy/milky bits, on a piece of glass inside the lens (it doesn't appear to be on the inside of the outer lens).