You asked
What percentage of the national debt has been generated by compound interest charges?
We said
Unfortunately ONS do not hold data of sufficient detail to enable us to estimate the percentage of debt generated by compound interest charges.
It may be worth noting that our published table PSA8A (General government consolidated gross debt), shows that gilts are the largest component of gross debt.. However the interest rate on individual gilts (like other debt securities) are fixed at the point of issue and so not subject to compound interest. Over the last 10 financial years between 94 and 98% of central government debt interest was paid on outstanding government debt securities (essentially gilts and treasury bills).
Published tables: https://www.ons.gov.uk/economy/governmentpublicsectorandtaxes/publicsectorfinance/datasets/publicsectorfinancesappendixatables110