Firstly an apology if this has been raised before.
I live in a rural area and have low broadband speed. I have been a BT Broadband customer for ages. BT have declined to permit me to register for BT Sport, because of the speed of the service available.
What I fail to understand is that presumably the BT box needs broadband to log in/ boot up (which it should be able to do), but does not need broadband to obtain the picture, which is delivered through the aerial like the other TV services.
If that is right, why do BT refuse to sell the box and service to me? I have been looking forward to the rugby for ages!
Are you sure? The BT website says this:
As long as you have BT Broadband and a BT TV package, you'll be able to watch BT Sport on your TV via your TV aerial (£10 viewing card and BT Vision+ box required).
I infer from this that the signal comes through the aerial, but it is controlled through the box.
Yes, BT Sport does come via the aerial with a viewing card for BTTV customers who don't have Infinity. I think your problem is that there is and always has been a minimum broadband speed requirement for BTTV to be provided.
I guess there is a minimum speed requirement because, if you can't use the BTTV IPTV services (and they can't sell you on-demand films etc to rake back the cost of the box they supply you), then they don't need your custom (& you may as well buy a Freeview+ recorder instead).
Remember that BT don't want to maintain the DTT service for long - it's an interim measure until FTTH is more widespread. They could sell CAMs for people like the OP to receive BT Sport, but they don't want to get into that game.