London councils lost 1,293 laptops, mobile phones and tablets over the last three financial years, according to a freedom of information (FOI) request.
Over the 2018/19 financial year, the 23 boroughs that make up the UK's capital reported 635 lost or stolen devices, more than double the amount reported in 2016-17 (304).
The FOI request, issued by the Parliament Street think tank, also revealed that mobile phones were the most lost item, with 951 going missing in total. That number increased by 122% over the three years, with 215 being reported lost in 2016-17 to 478 in 2018-19.
Additionally, 262 laptops and 80 tablets were reported as lost or stolen, with one of the worst offenders being Lambeth Council which reported 281 devices lost since 2016.
Richmond and Wandsworth saw a 666% increase in lost devices, reporting 123 and 170 devices respectively. Brent councils saw a 74% increase in reported lost or stolen devices and also lost a total of 143 mobile phones.
The report follows on from another FOI request made in December that highlighted the number of devices reported lost or stolen by the UK's police forces. The West Midlands Police were the worst offenders on that list, with 1,012 lost since 2016.
In 2014, a report into BYOD initiatives in local councils revealed that not all London boroughs had one in place. At the time, Camden had 252 personal devices activated on its network. It's worth noting that Camden was one of the councils that reported the fewest number of lost devices - 36 over the three financial years.
It was also revealed in 2015 that the NHS had also not put a BYOD policy in place. Reportedly two-thirds of trusts are risking data breaches because they lacked policies to manage what personal devices employees can bring in.
