In this article the Economist writes about the BoE:
"in the past decade the bank’s successive rounds of quantitative easing (qe), whereby it creates new money to buy bonds, have left it holding more than a third of the government’s entire stock of debt. That has, awkwardly, dragged it back into the realm of public-debt management."
From my understanding qe normally involves the buying of primarily government bonds. This would mean the BoE now has lots of UK government bonds. The bank of England is owned by the government so how is a government owning its own bond not just a promise to pay itself?