If Osborne misses his new target, there really is nothing left to cut

The chancellor's plan to run a surplus by 2020 is a cast-iron promise. If it goes off track, raising taxes or losing face are his only options

Napoleon would have approved of George Osborne. "I know he's a good general," the French emperor once said. "But is he lucky?"

The answer to that question, according to the Institute for Fiscal Studies, is yes. The chancellor got lucky when the Office for Budget Responsibility raised its forecasts for tax revenue and cut its predictions for interest payments on the national debt. That gave Osborne some much-needed wiggle room to delay welfare cuts, choke back on austerity and spend a bit more on infrastructure.

Related: Autumn statement: IFS warns on tax rises and spending cuts