Net interest margin (NIM) is a metric that banks love showcasing to shareholders and analysts, so unsurprisingly it is heavily manipulated. Whether by adopting their own accounting definitions or by heavy use of derivatives, they spare no effort to make NIM as high as possible.

Nowhere is this more prevalent than the UK, where leader of the pack is Barclays, with a NIM of 4% according to its latest accounts. Compare that to the US, where the biggest lenders struggle to achieve a NIM of half that figure. The numerator of NIM is net interest income which is hard to manipulate, so instead consider the denominator.