Incident: A bank's scheduled payments went out twice

Module 8 · Incident file · About 30 minutes

What happened

On Christmas Day 2021, Santander UK paid about 75,000 payments a second time. AFP, reported by Tech Xplore on 31 December 2021, wrote that "75,000 payments were made twice to recipients by about 2,000 corporate and commercial account holders", and that the bank was "seeking to recover £130 million ($175 million) it paid out on Christmas Day by mistake". CNBC (Sam Shead, 31 December 2021) reported the same figures and that the mistake affected Christmas Day and Boxing Day payroll.

The bank's explanation was short: "a scheduling issue" that it "quickly identified and rectified", and, from a spokesperson quoted by CNBC, "due to a technical issue, some payments from our corporate clients were incorrectly duplicated". The duplicates "came from the bank's own reserves", so no client lost money. Many went into accounts at other banks, and Santander said it would be "working hard with many banks across the UK to recover the duplicated transactions over the coming days".

That is all the sources say about the cause. Nothing below claims to describe Santander's systems.