The number of people being sent unsolicited sexual photos over methods such as AirDrop on trains has spiked, data shows.

Incidents surrounding the act known as cyber-flashing incidents have spiked, while authorities fear the crime is going "largely unreported".

Cyber-flashing is when a passenger sends an unsolicited sexual image on an iPhone using file-sharing function AirDrop.

Due to the technology's short range, victims are often targeted on trains where they could be in the same carriage as the often-anonymous perpretetor.

Reports of cyber-flashing to British Transport Police (BTP) have almost doubled in a year and campaigners say the number of incidents "will almost certainly be much higher".

Despite the rise there was only one arrest in 2019, according to the data obtained by a Freedom of Information (FoI) request.

First reported to the force in 2015, figures show that incidents more than doubled year-on-year in 2016, 2017 and 2018.

In 2019, there were some 66 reports of cyber-flashing - almost double 34 reports in 2018, and a large jump since 2016, when three incidents were reported.

Although numbers have leapt year-on-year, police believe it is still going under-reported due to victims believing the incident is "not serious enough" to speak to officers.

The data, from England, Scotland and Wales, shows there was only one arrest in connection with cyber-flashing made by BTP last year, which records incidents under their malicious communications act.

The force says the majority of incidents result in the failure to identify a suspect, due to difficulty in tracing the perpetrator.

In 2019, when the victim's gender was recorded by the force, the majority of those targeted (88 per cent) were women.

More than half (57 per cent) of those whose ages were taken by officers were aged between 21 and 30.

Most of the incidents were recorded in London, but reports were also received at stations in Birmingham, Warwick and Guildford.

Just under half (44 per cent) received an unwanted image on London underground services last year, while 40 per cent of incidents were reported at National Rail stations.

Rebecca Hitchen, campaigns manager at End Violence Against Women Coalition, said the increase shows women are becoming "more confident they will be taken seriously" if they come forward.

But she added: "It can also suggest that this particular behaviour is becoming more common.

"What we do know is that the actual number of women affected by this will almost certainly be much higher than the number of reports, and it will be impacting on their ability to go about their lives feeling safe and free."

Detective Inspector Ashley Cooper, from BTP, advised people to review their AirDrop settings to only receive messages from people in their contacts list.

He said: "As with other forms of sexual harassment, we believe that cases of cyber-flashing, which can involve the sending of unwanted, threatening or explicit sexual communications, goes largely unreported - either because victims don't feel the incident is serious enough to report or simply because they don't know where to turn.

"If you are a victim of cyber-flashing, our advice would be to report the matter to police as soon as possible."

Laws around image-based sexual abuse are being reviewed by the Government as part of a potential overhaul looking to bring cyber-flashing and other digital trends in line with other sexual offences.

The Law Commission will examine existing legislation to ensure it is keeping pace with advancements in technology, but is not due to report back until 2021.

A Government spokesman said: "It is illegal to watch sexually offensive material on our railways, and nobody should be made to feel uncomfortable or unsafe on public transport.

"We have asked the Rail Delivery Group to progress a package of measures to tackle unacceptable behaviours like this as quickly as possible."

Susie Homan, director of planning, engineering and operations for the Rail Delivery Group, said it was working with BTP to further improve safety and "tackle all forms of unwanted sexual behaviour".

Additional reporting by PA.