It happens while sitting on a bus. It happens when you’re walking up stairs. It happens sometimes without the victim realising, and it happens all too much.

“Upskirting” - when someone takes a picture up your skirt - is a form of sexual harassment that has been enabled largely thanks to smartphones.

It’s incredibly violating but it isn’t currently illegal in England, and one woman is trying to change that.

25-year-old Gina Martin was at BST Festival in London’s Hyde Park last month when she noticed a man’s phone screen with a picture of a woman’s thighs and underwear.

It was only when she looked more closely that she realised the woman was her.

Martin went to the police but was told there was nothing they could do because he’d done nothing illegal: “Unfortunately, I’ve had to look at the picture,” the police officer told her.

“It shows more than you’d like… but it’s not graphic. So there’s not much we can do because you can’t see anything bad. I’m going to be honest - you might not hear much from us.”

The only way an upskirter could be convicted as it stands is for “outraging public decency” or “voyeurism,” under section 67 of the Sexual Offences Act.

Had Martin not been wearing underwear, her case may have been treated differently, “but I don’t see how what I was wearing should affect their response,” she wrote for the BBC.

So Martin decided to start a petition, calling for upskirting to be made part of the Sexual Offences Act 2003. It now has over 56,000 signatures.

“Although the police were incredibly kind, the reaction was as bad as what that creepy man did to me – young women are not protected by the law when they ask for help,” Martin told the Standard.

“I think women in general are told to brush off something like having a pervy photo taken of you because it’s not a massive deal, but it’s harassment and it’s happening all the time.”

Her case has since been reopened by the police, but Martin is still fighting for upskirting to be made a criminal offence.

“Section 67 of the Sexual Offences act needs to be amended to label ‘up-skirt photos’ or ‘creepshots’ as a sexual offence. Period,” Martin says.

Upskirting is already illegal in Scotland, Australia, New Zealand and some US states, but England is lagging behind. In Japan, all camera phones make a noise when a picture is taken that cannot be turned off, in the hope of discouraging covert photography.

Some people go to great lengths to take upskirt photos, also known as creepshots. Men have been caught with cameras in their shoes, and dedicated upskirt photo websites exist too.

Martin has faced criticism by people who claim upskirting isn’t a big deal and the police should be dealing with “more serious” things, but any woman who has experienced upskirting will know how vile it is and how vulnerable it leaves you feelings.

22-year-old Leah from London is thoroughly on-board with Martin’s cause: “I think it’s so important that upskirting is made illegal, as to invade someone’s privacy for your own sexual gratification, without their consent, leaves the person feeling incredibly violated,” she told The Independent.

“For me it also made me feel really vulnerable - it happened on the London Underground when I was 19 and I felt so helpless that I didn’t know how to respond, I just got off the tube.”

Leading legal experts are also supporting the call for upskirting to be made a specific criminal offence:

“I would try to work it around a definition of voyeurism,” Simon Myerson QC told the Standard.

“At the moment it involves watching other people engaging in sexual activity and I would try and get a definition that says taking photos of someone’s underwear or private parts – making sure to be careful to exclude swimwear and tight leggings etc or you get into a murky situation – is an offence, unless the person gave their express consent.

“The ‘upskirter’ could then potentially have their card marked as a sexual offender and go on the Sexual Offenders Register.”

It would be a brilliant result for Martin and women across the world in the hope that upskirters would be discouraged.

A spokesperson for the Met Police said:

“The Met takes allegations of voyeurism seriously and does and will investigate them thoroughly.

“We use a range of policing tactics and deploy officers on specific operations to target this sort of criminal behaviour based on intelligence. We understand that it can be incredibly invasive and distressing for those that this happens to.