Departments can make efficiency improvements up to a point, but eventually ever-smaller budgets make it difficult to provide core services.
From prisons to the National Health Service, measures of performance started to go south from around 2014, according to a recent report from the Institute for Government, a think-tank.
The rate of child poverty, which fell during the 2000s, is now rising sharply, in part because of big cuts in working-age benefits.
Since the election in 2015 the government has subtly adopted a new approach to austerity: less emphasis on spending cuts, more on tax rises.
In the average budget or autumn statement since then, the government has called for tax rises four times as big as the average in the parliament of 2010-15.
Granted, the personal allowance for income tax has risen.
The headline rate of corporation tax has been cut.
Yet increases in less-noticed charges such as environmental taxes, stamp duty (a levy on property transactions) and insurance-premium tax (levied on everything from holiday to vehicle insurance) have more than compensated.
Mr Hammond is fast gaining a reputation as a tax-grabber.
In his first budget in March the chancellor pencilled in a reduction in the tax-free allowance for dividend income from 5,000 pounds to 2,000 pounds.
He also proposed an increase in the national-insurance contributions paid by the self-employed—though this was hastily, and embarrassingly, withdrawn after an outcry from newspapers and Tory backbenchers.
In all, following recent revisions to official economic forecasts, it is now expected that in 2018-19 the tax burden, expressed as a percentage of GDP, will be at its highest level since the mid-1980s.
Mrs May's “instinct” may well be to lower taxes, but she cannot help being bound by Britain's unforgiving fiscal arithmetic.