If it was in your home made compost, it must be something you grew last year, have a look back, it may come to you.
In the sticks near Peterborough
Not necessarily; if your food waste goes into the compost bin, it could be a seedling of anything you bought to eat which had seeds in. I agree with those who've said it looks like the solanum family, though not potato or tomato. So aubergine is a possibility, if you eat them. Why not plant it in a pot and see what comes of it?