What are the economic constraints that will underpin the chancellor’s spring statement – and why does she sees them as vital?

As Rachel Reeves faced a backlash over government plans unveiled last week to slash spending to balance the books, the chancellor and Treasury repeatedly argued that difficult decisions were necessary to avoid breaking the fiscal rules she adopted last October.

But what exactly are these constraints, and why does Reeves believe them to be so important? In the build-up to Wednesday’s spring statement, why are many economists urging her to flex or even rewrite them, as chancellors have on several occasions since they were first drafted by Labour nearly three decades ago?