It's a medlar and makes lovely jelly.

yes I agree its a medlar.

Not ripe enough to make Jelly with yet though. You need to wait until they are just going soft, but before they rot. To eat raw they need to rot down to really soft (bletting). HenryV111's favourite fruit.

Don't they stink when they're bletted? I know someone who's got these but says she cannot bear the smell...

They only smell if they are going mouldy rather than 'bletting'. At least they do to me. I don't like the taste of them then either, though the jelly is nice.