Following a google, I think we had a pumpkin plant in the garden.
But initial 'on the spot' diagnosis was courgette... So when I spotted a huge green ball just now asked Mrs Nutty what it was. "Must be a marrow as we haven't picked the courgette", she said. When she looked to see if it was ripe, 'it came off in her hands'....
Definitely not a marrow, as it's a green ball 7 inches in diameter, hairy, and a mottled green colour as opposed to stripy white and green.
Google images show the plant and fruit as pumpkin plants. (The internet which cannot lie, also states that pumpkins are ripe by the end of august).
So, considering we now have this on the kitchen windowsill. Can it be eaten? What recipe to use?