The number of girls being forced into marriage ahead of the summer holiday period has increased by more than a third in recent years, according to a leading charity which has accused the government of an abject failure to get to grips with the problem.

Karma Nirvana condemned the Home Office for shelving a campaign raising awareness of the practice, which sees girls taken abroad to be married off to strangers, in the "critical" run-up to the summer break – the time of the year when the problem is at its peak.

Speaking exclusively to The Independent, the national charity – which provides training to the police, NHS and social services – revealed it learned of 150 new cases of forced marriage from May to July, a rise of more than a third on the figure seen in the same period in 2015, when it received 99 new cases.

The charity also found cases of forced marriage soared by 40 per cent at the start of the school holidays this year, and revealed it was receiving reports of cases at a rate of two a day in July, more than double the average of 25 seen in the first four months of the year, with 44 cases reported in May and June.

And the figures do not reflect the full scale of the problem, as forced marriage continues to be starkly underreported – with the Home Office describing it as a "hidden crime".

Jasvinder Sanghera, CBE, founder and chief executive of the charity, warned thousands of girls would not be returning to school in September, having had their educations cut off and – in many cases – been left trapped in a cycle of poverty after falling victim to the offence.

Ms Sanghera, who set up the charity in 2008 after escaping a forced marriage by running away from home aged 16, demanded that sex within such unions be treated as rape.

She said the Home Office had planned an awareness campaign ahead of the summer holidays but decided to drop it at the last minute, postponing it until later in the year, a strategy she said was "missing the point".

She said the pre-summer holidays campaign had been running for the past few years and would have seen the Forced Marriage Unit work with police and local authorities to raise awareness of the problem. She explained the campaign would have used social media and disseminated posters, literature and information about helplines with the objective of increasing the number of victims coming forward and raising public understanding.

“It was wholly irresponsible of the government to drop a campaign devoted to awareness, pre-summer holidays. This is the most critical time of year,” she told The Independent.

“There will be thousands of children across Britain that are now being prepared for engagements and forced marriages in Britain and [who] will be taken out of this country over the summer break. The family use the opportunity of this long holiday to marry them off.”

Young girls are often told they are going back to their country of origin to visit family, and remain unaware of what is happening until they arrive.

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“We have heard of cases where people are engaged or married and just think it is a party, and do not realise until afterwards,” she said.

“There is no doubt there will be thousands of girls across Britain who will not return to school in September. You are talking about people under the age of 16, and [aged] 16 to 18. When it comes to September, teachers will notice they are missing but the alarm bell will not necessarily ring because the first person to be alerted are the parents, who will often say they are being educated abroad. The parents are the perpetrators of the crime of forced marriage. The parents' story will be heard and the victims' will not.”

Laws making it illegal to force someone into marriage in England and Wales were implemented in 2014. Anyone found guilty of doing so can be imprisoned for up to seven years.

Ms Sanghera, who also acts as an expert witness and lobbies government, said her organisation had found schools are often reluctant to work on the issue of forced marriage, despite being in a good position to help prevent it. She said she had contacted schools in Luton and Tower Hamlets, but they had ignored her outreach efforts.

“Very few schools are willing to engage. We write to them and we go into the school and a survivor does a presentation – on average we receive three disclosures [of forced marriage] for every school we go into," she said. "We went to one school in Birmingham and within seven days of being there we had dealt with over 11 disclosures.”

She said the charity has heard “the most distressing” stories which displayed a dearth of awareness among teachers and social workers. She added teachers often view the issue as a cultural one, and fear it is not their place to intervene.

“After they have heard the presentation, teachers will come up to me and recall multiples cases of girls going missing and say ‘I just thought it was cultural’. Some will say ‘I did raise it but it wasn’t taken seriously. I was told: 'It’s their culture, respect it’'.”

The charity CEO said it was difficult for victims because they have never heard a counter narrative to their parents' plans for forced marriage – and argued they are subject to years of conditioning at home.

She also drew attention to the fact forced marriage is a hidden crime and is vastly underreported, adding: “Even government say that we are dealing with the tip of an iceberg - we are seeing just a scratch on the surface.”

(Jasvinder Sanghera)

A teacher at a secondary school in Islington said she had not received any training from the school she works in about forced marriage. She also said she had never been told to be specifically alert during the lead-up to the summer holiday break.

“I don’t think I’ve ever been told to in particular look out around the summer holidays for forced marriage,” the teacher, who asked to remain anonymous, told The Independent.

“The training that school staff receive to help them spot these issues is really poor, meaning that a lot of people who work in schools have no idea how to even recognise that it is happening.

“Rather than there being any attempt to understand a different culture or why this happening to young girls it often becomes this very uncomfortable anti-Muslim conversation. Ultimately the really crap training that school staff get around this issue only puts these kids even more at risk because nobody knows what to look out for.”

This echoes research by the Association of Teachers and Lecturers (ATL) from last year which found less than half of teachers said they had been given training to recognise the signs of forced marriage.

Rubie, a forced marriage survivor who is now in her 30s, said she was forced to leave the UK during the summer break.

“I and my younger siblings were taken to Bangladesh for the summer holidays but ended up staying there for 11 months in total,” she said. “For the first six months, I enjoyed exploring my culture and the experiences of my parents’ homeland; this was until my father told me that I would be getting married. Unknown to me, all along I was being held like a prisoner.

“I soon got married to a man twice my age, I got raped until I became pregnant as a guarantee for his child to be British born - to enable him to come over to the UK.”

Rubie, whose Bangladeshi parents moved to the UK in the 1970s and lived in Wales, then became seriously ill and returned to the UK, where she tried to kill herself.

“I tried to take my own life," she said. "I didn’t succeed and became desperate so I ran away from home with another man and had a second child from an abusive relationship. I lived my life in a dysfunctional way and became very depressed.”

She has spent the last six years investing in education. The survivor, a member of Karma Nirvana’s survivor ambassador panel, said: “I have started to enjoy my life and work towards achieving my passions and hobbies, which I did not have before.”

Helen Porter, who chairs the ATL’s equalities and diversity committee, also rang alarm bells about the issue of forced marriages spiking during the summer holidays.

Ms Porter, a teacher for 30 years, told The Independent: “It’s an erosion of the girl's human rights if she is being taken from education and being forced to marry someone she is not choosing to marry. As a teacher, you know your pupil’s aspirations and ambitions and suddenly it’s all over for them. Her life chances are greatly reduced.”

She argued the disappearance of girls has huge repercussions for their peers and the wider school community – with people left “disorientated” and “upset” by their absence.

A Home Office spokesperson said: “The UK is a world leader in tackling the horrendous crime of forced marriage, and work to tackle it is an integral part of our cross government violence against women and girls strategy.

“We continually work with charities and police to highlight this important issue to the public and the work being done to tackle it, via the media and community engagement.

“[The] Border Force, the police and other agencies also regularly work together to raise awareness of harmful practices, including forced marriage, through joint operations aimed at individuals travelling to or from the UK, to countries where these practices are prevalent."

The Home Office said it was aware the school holidays may be a period of increased risk. It said earlier this month Border Force officers at Birmingham Airport had been leading an "operation to detect, intercept and provide assistance to potential victims who may be travelling abroad for the purposes of having FGM [female genital mutilation] conducted on them and/or being forced into a marriage overseas".

The Forced Marriage Unit (FMU), a joint unit of the Foreign and Commonwealth Office and Home Office, leads the government's forced marriage policy, outreach and casework.

The FMU gave advice or support related to 1,196 possible forced marriages last year.