A drone was confiscated earlier this month after it crashed at a north London jail with drugs and cell phones, according to police. The drone was not alone: Another was seen later that day and caught mid-flight.

The drone seizures followed a man acting suspiciously near the prison just one day before the drones were caught. That man ran from police when confronted, dropping two bags of drugs and phones, according to the BBC. No arrests have been made so far in connection to the drugs, phones and drones.

“We are able to intercept them thanks to the vigilance of officers and the public,” Chief Inspector Steve Heatley said. The drones “carried a substantial amount of Class B drugs, legal highs and a large quantity of mobile phones.”

A recent study found that drones are becoming a go-to tool for drug smugglers looking to get their product into prisons and jails. In England and Wales, the study found, drones were becoming more and more popular amongst smugglers. In 2015, there were 33 incidents of drones carrying drugs across fences and walls compared to just two in 2014 and none recorded in 2013. In those studies, the drones mainly carried drugs, phones, phone chargers and USB cards.

The Ministry of Justice in the U.K. has said that more should be done to stop the drone problem.

“We work closely with the Prison Service to gather intelligence in order to carry out proactive operations to arrest and prosecute such offenders,” Heatley said following the most recent round of drones.

Around the world, the rising popularity of drones has been a cause for concern. Nearly a million drones were expected to be sold in the United States alone last year, marking a 63 percent increase over the year before. Drones can pose significant problems and not just for prison guards hoping to keep their jails drug-free. Aviators, too, are concerned that the unmanned vehicles may hit planes and cause issues.