Sorry to Burst your bubble Pr00ne but...
The government Only 'owns' about a third of the debt. (BofE). About a third is owned privately and another third is owned by foriegn nations.
If the government were to write off its debt the pound will be extinct as a tradeable asset. THAT is why this is important and THAT is why you are wrong. Claim all you like that government finances are different (to some degree they are -no private bank would lend so much to an individual without collateral) but in the end the Piper gets paid or you go broke. Now, the government CAN print its way out, but that is called HYPERINFLATION. Try Weimar germany in the 30's or Venezuela right now.
Hyperinflation is basically a debt default in disguise. Anyone with 'money' in the bank gets screwed big time. Cyprus a few years ago anyone?
Sorry to be a doom and gloom but this is factual.