Sky LLU has a max upload of 1.3Mbps, they don't use Annex M to offer anything higher.
There are also lots of people having issues whereby Sky's DLM has a profile which caps the upload at 799kbps for "stability" reasons, even where it's been stable for months on end at higher speeds.
Sky's DLM system will profile to a max of 2.5Mbps
Now this will require a router that supports Annex-M,
Sky Hubs will not support this so the most you will get on that router will be 1.3Mbps.
Have to say I changed to a netgear I had been sent for testing but that seems not to support Annex-M
Also should point out that with the 2.5Mbps some lines are very unstable due to max delays being 1ms among other things, however my line is rock solid ( yes I am only on 1.3Mbps up but I have seen others being unstable )
I wasn't aware their DLM took the upload rate as high as that. When I was on BE There I was getting 2.8Mb upload rate on 3db and near max download rate.
I thought Sky only provided 1.3Mb max.
The additional bandwidth will be handy in the interim before I move to a fibre solution.