What you're missing is the fact that having a mortgage implies having an asset (a house) worth something more than the mortgage principal. The government does spend on investment, but the vast majority of the budget in sunk into running costs. Then, the more appropriate comparison would be a £25k earner with £57k in credit card debts, which is obviously a lot more scary - but again not completely comparable as the guy would be paying 20-30% interest while the government pays close to 0%, mostly because they have the power to raise their income on demand if they need to in order to service their debts.