If you're worried about the national debt burden, then what follows is one of the scariest graphs from the IFS's Green Budget. It extrapolates from the government's current plans and assumptions to work out when debt may get below 40 percent of GDP again. The answer, as you can see, is sometime in the early 2030s - and later if you account for demographic pressures:
Of course, this isn't a perfect model. For instance, things will certainly change before the 2030s - governments will come in which adopt stronger or weaker fiscal tightening policies; we may have another recession or strong spurts of growth; and so on. But, even from the vantage point of 2010, it's clear that Brown's debt binge will haunt us for decades to come.
P.S. The Green Budget is available here. It's worth reading through the presentations on the right-hand side of that page, as well.