If it's not being explicitly forwarded to your PC, then it's almost definitely blocked by default at your router. Otherwise it would be an open route into your network.
I doubt BT universally block anything inside their network before it gets to your router.
I guess I'm in an odd position that my internal IP at work is actually my external IP and as far as I know there none or very few restrictions on ports.
I was talking more about the ISP managing the router, but yeah, I'm forever being prevented from FTPing and such. And it's a fucking miracle if my Lync client works.