The link to the BoE speech[1] is worth reading. If they use a common ledger to enable other firms (like P2P lenders) to move reserves between each other and banks then that's a game changer (well, so long as they get rid of the FSCS[2]) as banks will be in fear of losing reserves - so they'll have to be nicer to their depositors. It doesn't matter that the ledger's under control of the central bank, at least not to the man in the street.

Is it a threat to bitcoin? They are making disparaging remarks about bitcoin but that's to be expected and a good sign as it means they are taking it seriously. Competition is good, isn't it? Thus RSCoin's good for bitcoin and bitcoin for RSCoin. So maybe bitcoin now needs to up its game if it wishes to survive, not bury its head in the sand.

[1] http://www.bankofengland.co.uk/publications/Pages/speeches/2016/886.aspx
[2] http://fscs.org.uk/