Works with Draytek 2750 on latest firmware 21.5.3, apparently. Not tried it, but my mate has it working, something to do with IGMP V3 proxy settings. I am sure he found the solution on this forum.
He says "turn on IGMP and IGMP snooping on 2750 and Sky Sports on BT Vision box works fine", but as he is on a train at the moment heading up to the North (Liverpool...) can't remember the exact settings, but only worked/appeared in later firmwares.
Just came back again, might be settings on 2850 as well. He currently has two Infinity lines in his house, home and a business one, both feed into a 2850 where they are shared between home and business use and Sky Sports on BT vision box works on home section of network.
But convinced he had it working with 2750 before he changed to the current 2850, only a month or two ago.
i read somewhere on these forums that someone got thier router to work by lowering the MTU slightly, not sure if they did anything else, i forget the exact post