* Brad Pitt accompanies Angelina Jolie to sexual violence summit
* Celebrity power credited for putting issue on world agenda
* Britain says governments must act and be held accountable
Dressed in black, Pitt and Jolie flanked Hague at the opening of the third day of a four-day summit in London that is the culmination of two years' joint work by the actress and Hague.
Up to 1,200 government ministers, officials, activists and members of judiciaries and militaries from more than 120 countries are at the summit that aims to find practical steps to punish those responsible for sex violence and help victims.
Hague said his partnership with Oscar-winning Jolie, special envoy of the UN High Commissioner for Refugees (UNHCR), had put the issue of sexual violence in conflict on the world agenda and was an example of how foreign policy could be conducted in the future.
"She brings what governments can't ... (as) there was no really big government of the world driving this," Hague told a small media briefing including Reuters.
"You need something much more than government to be able to reach people who don't easily listen to governments and Angelina brings that, as well as having great knowledge and passion about these issues."
Jolie's involvement in humanitarian issues dates back to 2001 when she travelled to Sierra Leone as a UNHCR Goodwill Ambassador and saw the impact of years of civil war when an estimated 60,000 women were raped.
Her link-up with Hague came after he contacted her on seeing her 2011 directorial debut "In the Land of Blood and Honey" set against the 1992-95 Bosnian war in which more than 100,000 people were killed and an estimated 20,000 women believed raped.
"MEN NEED TO SAY NO"
The actress, 39, has attended the summit since the start on Tuesday but her partner, Pitt, joined her for the first time on Thursday for the opening plenary.
"We, as an international community, have never done enough to stop this abuse and we do survivors a disservice when they know we are aware but do nothing to hold the perpetrators accountable," Jolie told the summit on Thursday.
"Today we have an opportunity to begin to change that."
Both Jolie and Hague have stressed the importance of ensuring the summit is not just a talking shop but the start of action to shatter a culture of impunity over sexual violence.
The summit follows a series of shocking cases of violence against women including the kidnap of 200 Nigerian schoolgirls, the stoning of a pregnant Pakistani woman to death, and the gang-rape and murder of two Indian girls.
Last year Hague and Jolie launched a declaration, now signed by about 150 countries, pledging to pursue those responsible for sexual violence and provide justice and safety for victims.
This week they launched a international guide on how to investigate such crimes, collect evidence and prosecute.
Nkosazana Dlamini Zuma, chairwoman of the African Union Commission, said it was vital that attitudes change as "without men saying 'no,' we will not end this cycle".
Hague said now it was up to governments to take action and for the public and activists to hold them accountable.
"Together we can unleash a wave of practical action through the world that will make a huge difference to the lives of men, women and children in conflict zones," he said.