I'm not making it up...it's information that's readily available in any article from the budget.
It simply cannot work!
It can, if government bonds are maturing in a given year and are cumulatively worth more than the value of the budget deficit; then yes the deficit is adding to the national debt, but government bonds maturing are also paying it off...to put it simply, there is going to be a point where we start paying back more than we borrow and at that point, national debt will begin to fall.
National debt as a % of GDP is of course the main thing as you say, but it's deficits that get markets twitchy, not the overall national debt. As I say, as soon as the budget is neutral, real terms growth will return to government departments.