A Foreign Office team specialising in gathering evidence of sexual violence in conflict zones has yet to be deployed to Myanmar’s refugee camps despite evidence that systematic mass rape has been used as a weapon by the Burmese military against the Rohingya muslim minority.

The specialist group was set up by William Hague as foreign secretary in 2012 as part of his joint effort with the actor Angelina Jolie to highlight the pervasive use of sexual violence in conflict. He regards the initiative as one of his chief legacies.

The Foreign Office (FCO) has said it is still assessing the need for a team, even though aid agencies have reported the mass use of rape, including of children as young as 10. The burning and violence in Rakhine state started at the end of August and the FCO minister Lord Ahmad has described reports of sexual violence against the Rohingya as “staggering”.

Hague and his former special adviser Lady Helic have written to the FCO to demand to know what it is doing to investigate and document rape allegations against Burmese forces.

As many as 600,000 refugees have fled to Bangladesh, with aid agencies, such as Doctors without Borders and the International Organization for Migration, reporting hundreds of cases of rape and sexual violence amongst refugees.

The FCO is supposed to have a roster of health experts on standby ready to travel to war zones to investigate allegations of sexual violence, and to gather evidence that could be used in international criminal courts. The experts were deployed in Syria, South Sudan, Libya and Bosnia.

The team of experts consists of health specialists, lawyers, police officers, psychologists and forensic scientists. It was set up in 2012 to help local authorities where crimes of sexual violence were reported and local bodies did not have the capacity to help.

The team is expected to prevent evidence of sexual violence being lost, compile documentation and to identify perpetrators and ringleaders. By 2013, the foreign secretary had recruited more than 70 experts.

One source said: “The Foreign Office appears [to be] very good at revising strategy papers … but less good at doing anything about it. The issue is incredibly urgent, and the team was set up for precisely these purposes. The evidence has to be gathered now, and not when a bureaucracy is ready to do so. The long-term psychological damage of sexual violence, including the attached stigma, is so dreadful. It can damage relations within a family sometimes for even longer than a death.”

In their joint letter, Hague and Helic say the international community has a responsibility to ensure rape is never used as a weapon of war to intimidate humiliate and persecute ethnic minorities.

Before the current violence, efforts to criminalise rape and protect women by law in Myanmar foundered, despite efforts in the Myanmar parliament.

The FCO said it was assessing what support the UK might provide at Cox’s Bazaar, the main refugee site. The Department for International Development has provided £47m in aid, but none earmarked specifically to address the issue of sexual violence.

The FCO minister Mark Field was also one of the first European ministers to reach Rakhine state, even though he was not allowed to visit the border. He has described the behaviour of the Buddhist forces as ethnic cleansing.

Many of the refugees do not wish to return because they do not feel safe, and there is a dispute between Bangladeshi and Burmese authorities whether their return is even possible.

Field has said “unless we get repatriation at an early stage, the perception from the Burmese military – and in the international community – will be that they have got their own way. It is, in my view, of utmost urgency to get some repatriation – we need to do that – but part and parcel of that is having villages in which people can live. Many have been burned. Rebuilding will not necessarily take quite so painstakingly long, provided that the international community has access to Rakhine.”

Aung San Suu Kyi, the leader of the ruling party, has been widely criticised for her failure to condemn the behaviour of the military, but her defenders claim that in a hybrid regime in which the military dominate the major ministries, including the responsibility for borders, she is walking a political tightrope.

She visited Rakhine state last week for the first time since her National League for Democracy was elected in 2015, and last month set up a new national aid body that she will chair to hasten long-term development to reduce poverty in Rakhine, one of the poorest areas of Myanmar.

One of her advisers, speaking on condition of anonymity, said “if sanctions are imposed it will have cataclysmic consequences for her, and no one so far I know has a plan B for Myanmar”.

The pope is also due to visit Myanmar at the end of this this month in his first visit to a predominantly Buddhist country and her advisers see the visit as “an immense opportunity to combat the role hate speech is playing in the country”.

“People in the country recognise the religious language she has been using, so people understand she is trying to appropriate language of religion hijacked by religious extremists. So much of this has been fuelled by the language of hatred. Freedom from hate has become almost her new version of freedom from fear.”

Her advisers say: “In her speeches in September and October she had tried to define what a national Burmese humanitarian effort might constitute, and the fact that excluded the military, seen as the guardians of Burma since 1940, is very significant. Until the constitution is changed there can be no settled democratic future for the country.”

Dfid stressed that much of the £47m it is now providing to help refugees in Myanmar will go to help victims of sexual violence. “UK aid is helping to provide counselling and psychological support that will reach over 10,000 women suffering from the trauma of war and over 2,000 survivors of sexual violence,” it said in a statement.

It added it was supporting the International Organization for Migration (IOM) to operate five mobile medical teams and five health posts to help address gender-based violence.

• This article was amended on 7 November 2017. An earlier version misnamed the International Organization for Migration as the International Office of Migration.

