"In a club I've been picked up, held with my legs in the air and groped from behind," says Lisa Clarke, one of the campaigners behind No More Page 3. "I couldn't get my feet back on the floor and the people around me did nothing."

Nightclubs are a hotbed for sexual offences, according to an NUS report. And many students see groping as a normal but unwanted part of a night out.

From suggestive comments, to groping and grabbing, sexual harassment is defined as behaviour that is unwanted, intimidating or humiliating for the victim. But many students don't think anything will be done if they report it.

"There's a culture in club life that accepts it as the norm and if you're not ready to accept that then that you're not welcome," says Clarke.

But things may be about to change. A number of popular London venues, and the University of London students' union, have signed a pledge on sexual harassment, to tackle the problem head on.

Those involved include the popular Fabric, which holds regular student club nights, and Ministry of Sound. Also signed up are trendy East London venues such as Dalston Superstore, Alibi and Birthdays. Student unions, including Royal Holloway, Kings College London and Soas, have also shown an interest in signing the pledge.

Night club promoters have been criticised in the past for their advertising. The NUS found in their report that a number of clubs used images and messages that could be seen to encourage harassment and assault as part of their promotion strategy.

"If you look at some of the nights that are aimed at students, a lot are centred around sexual harassment and sexism," says Clarke. "There are nights where people are told to dress as 'CEOs and corporate hoes', and language like 'bag a slag' is used in adverting."

Last year a student club night in Leeds even went as far as to release a promotional video that encouraged male students to "rape a fresher".

The new pledge aims to stamp this out and to encourage a more positive attitude towards sexual offences.

Brought about by street harassment charity Hollaback London, and supported by Everyday Sexism and the End Violence Against Women Campaign, the pledge uses the strapline "good night out". It is the first coordinated approach to sexual harassment across clubs in the capital.

Venues that sign up agree to put posters in visible places that say: "If something or someone makes you feel uncomfortable, no matter how minor it seems, you can report it to any member of our staff and they will work with you to make sure that it doesn't ruin your night."

As part of the pledge staff will be given extra training about spotting and handling sexual harassment. "We want people to feel that if something happens, the staff are on their side," says Bryony Beynon, co-director of Hollaback London.

"Having your bum groped in a club is common, as is people not taking no for an answer and being overly persistent. People often just say 'that's what everyone comes here for'. But people want to go out with friends to dance and have fun."

The training will teach staff that if one person reports something, it's probably happened to four or five other people as well. Staff will also be reminded that young people tend to minimise their own experiences to avoid making a fuss – but they should still be listened to.

Jake Gill, manager at Alibi in Dalston, says: "People have bad experiences with doormen and barmen not hearing them out. We wanted to let people know that we're not going to stand for it."

Hollaback encourages students to tweet and let them know if they feel that the pledge is not working. "We're aware it's easy to put a poster up, but a lot harder to change assumptions that can be pretty ingrained," says Beynon.

"We want feedback. So if there's a poster in a venue, but you report being harassed or assaulted and nothing happens, tweet us and let us know. It's a practical campaign and we want to see proof of it working.

"So far, we've had a good response: people who work in clubs have said that it's long overdue and is exactly what they need. Students and clubbers have told us that they wished the posters had been up when something happened and they felt like they couldn't report it."

If the campaign works, Hollaback hopes to talk to more clubs and student unions around the country.

• To find out more about the campaign and see the full list of venues involved click here. Let us know what you think of the campaign in the comments section below.