A third risk to banks from higher rates is that more of their customers will struggle to repay their loans. Quantifying this risk is difficult since loan losses are influenced not just by interest rates but also by economic growth and employment, both of which would need to improve for central bankers to dial back their interventions. Even so, there are worrying signs. In Britain almost a fifth of secured loans have gone to households that have less than £200 ($307) a month left after paying essential costs, according to the Bank of England. Higher rates could push many into default. The dilemma for policymakers is that keeping rates low for long is dangerous. So is letting them rise too quickly.