David. As GDP is not a particularly accurate figure, some of it being completely made up, e.g A rental figure is calculated on houses in private ownership when no rental ever takes place, the figure of 100% of GDP is a bit meaningless.
'Borrowing' is not the right term to apply to government bond sales. It's the safest investment that any individual or institution can make, because the government will always pay the interest on its bonds and the principle if the bond owner wants their investment back. But most bondholders don't want the principle back Just ask the folks on the Premium Bond threads if they want the government to repay them the money they've invested in them!
The UK government has never, in 300 years, reneged on payment of interest or principle. There's no reason why it should, it can always create the money to pay it.
The 'yield' is an artefact of the secondary bond market, which is just a vehicle for speculation, the same as stocks and shares. The interest payable on a bond is different; the government pays only whatever interest it put on the bond when it sold it.
Any attempt to cut the 'debt' is pointless.
Of course, the government, instead of issuing bonds 'could' just run up a theoretical overdraft at the BoE, but convention and practice (and when we were in it, the EU) doesn't allow it.