Thanks for posting that, the key can be seen in 2009, where the budget deficit more than doubled, as the wheels came off in spectacular fashion. You can see where the Brown Chancellorship started throwing money away as far back as 2002, ending in the disaster of 2008-9.
Think you will find that 2008-9 deficit was because Banks had to be bailed out to keep the country afloat.
What is noticeable is that Denis Healey brought the Net Debt as a % of GDP down and yet it didn't move further down by much for 10 years, then it jumped in mid nineties and under Gordon Brown it was lower than under post Thatchers Govts.