Transport for London say 90% of sexual behaviour on the capital's transport network goes unreported.

BBC 100 Women went undercover on the Tube with British Transport Police officers trying to catch offenders.

Read what to do if you are being harassed here.

Video journalist: Chris West; Producer: Georgina Pearce

BBC 100 Women names 100 influential and inspirational women around the world every year. In 2017, we're challenging them to tackle four of the biggest problems facing women today - the glass ceiling, female illiteracy, harassment in public spaces and sexism in sport.

With your help, they'll be coming up with real-life solutions and we want you to get involved with your ideas. Find us on Facebook, Instagram and Twitter and use #100Women