A woman who was allegedly sexually assaulted on the London Underground has condemned the fact there are no CCTV cameras on the Tube line where the incident happened.

Campaigners say it is “very worrying” there are no CCTV cameras on either the Central line – the line on the London Tube where the highest number of sexual assaults take place – or the Bakerloo line.

A 23-year-old woman, who asked to remain anonymous, said she was sexually assaulted on the Central line on her way to work at 8am last week.

She said: “It was rush hour and I was the second closest to the door but a man was behind me. I thought it was his bag brushing against me but then I realised it was an erection. I felt his groin on me. He grabbed my waist to bring me closer to him. I am 5ft 3in and he was about 6 ft 2in. I was in such shock. My brain was not working.

“When more people got on the train, he had to stop what he was doing. I was looking at him and I was teary-eyed. I tried to take a photo of him – either stupidly or bravely. My hand was shaking. But he put his arm over his face.

“When we got to Liverpool Street, I got off to try and take another photo of him but he ran away up the escalators so I gave up chasing him. By that point, I broke down crying and went to ring my dad to tell him what happened. I have been feeling awful, anxious, upset, angry and confused since then. I have had panic attacks on the train.”

The young woman, who said she got the sense the man had sexually assaulted women before, said she went straight to the British Transport Police to report the incident.

She said: “The police officer said, ‘I know this isn’t any consolation but this is a regular occurrence on the Central line. He said, ‘There is no CCTV on the Central line so the men know they can chance it’. But this is ridiculous – find a solution. I called Transport for London. I was fuming.”

She said when she asked both the police officer and then the person from Transport for London why there was no CCTV, they both told her it was because the trains are old. The police advised her against taking the case to court due to not having CCTV footage, she added.

“Luckily, work have said I can come in later so I don’t have to get on the same train as him. But why is it me having to change my daily lifestyle and my way of thinking?” she said. “Now when I see schoolchildren getting on the Central line by themselves, I feel worried for them.”

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Figures taken from reports made to the London transport network’s flagship text message service between July 2016 and January 2018 show there were 348 reported incidents on the London Underground alone, of which 100 were on the Central line – nearly double that of the next most reported line, the Victoria line at 55.

Rachel Krys, co-director of End Violence Against Women, said: “We know the perpetrators of sexual assault do it repeatedly and they learn where it is safe for them to do it and where they are not going to get caught and they use that to victimise and assault women.

“It is not accidental. It is perfectly possible to stand next to someone and not assault them. It is not always opportunistic. We are talking about predatory behaviours and people who use the system in order to assault women.

“We need a concerted effort by TfL and the police to make sure there aren’t no-go areas for women on public transport. The entire transport system should be a no-go area for men who sexually assault women.”

Sian Berry, the co-leader of the Green Party who has been a London Assembly member since 2016, said: “More people use buses but the proportion of sexual assault on the Tube is so much higher. This is possibly because it is an enclosed space.

“Perpetrators are probably not doing it on the way to the work and will be targeting the Tube – a lot of people are serial offenders. If they are targeting lines that don’t have CCTV, that is very worrying – and that is why it is so important people report. It should be a high priority to introduce CCTV. If there was a safety issue that might cause trains to crash, they would deal with it. This is a safety issue as it can harm passengers. It needs to be dealt with, with urgency.”

The Central and Bakerloo trains are the only two underground routes without onboard CCTV. While TfL says the former line will be equipped with CCTV by 2023, they could not give a date for the Bakerloo line.

Siwan Hayward, director of policing for TfL, said: “There is an extensive network of more than 77,000 CCTV cameras operating across London’s transport network, with 3,000 police and police community support officers dedicated to catching offenders. Anyone who experiences or witnesses a crime should report it immediately by texting 61016, as every single report matters and helps build a picture of the offender so they can be caught and brought to justice.”

They said all of their passengers have the right to travel without fear or intimidation and they were aware that for too long these crimes have gone unreported, but their Report It to Stop It campaign had meant the number of people reporting these “disgusting crimes” is increasing.

A representative for British Transport Police confirmed they were investigating the alleged assault.