Hundreds of vulnerable children as young as 10, who have spent most of their lives in the UK, are having their applications for British citizenship denied for failing to pass the government’s controversial “good character” test.

Figures published by the Home Office after a freedom of information request by the Guardian show that, on average, one child a week has had their application rejected over the last five years – with campaigners estimating that as many as 400 have been denied citizenship for failing to satisfy the good character requirement since it was introduced in 2006.

In some cases, children who were born in the UK have been turned down on the basis of convictions for crimes as trivial as petty theft, with even offences that are punished with a caution or a fine considered serious enough to warrant their rejection.

Critics say the figures are evidence of the Home Office failing to meet its statutory responsibilities to promote a child’s welfare and making the “best interests” of the child a primary consideration in these applications. They criticised guidelines for failing to differentiate between young people who have grown up in the UK and want to register as British citizens and adult migrants looking to naturalise.

“These are not adult migrants,” says Solange Valdez-Symonds, the director of the campaign group the Project for Registration of Children as British Citizens (PRCBC), adding that young people should not be put in “a position where the secretary of state thinks or believes they can be removed to some obscure country where one of the parents or both parents were born. It’s not acceptable, it’s outrageous and an insult to them and the society of which they are members.”

Valdez-Symonds, who has supported more than a dozen such cases, describes her clients as particularly vulnerable children. “All the clients have been destitute or very poor. At least half are looked after children or have had some sort of social service intervention. All of them are black,” she said. “The whole thing has a big impact on BME [black and minority ethnic] children.”

Liz Barratt, the joint head of immigration at the London law firm Bindmans, said her clients affected by the good character requirement were young people who had had “quite disruptive childhoods”, many of whom had been in the care of local authorities. She added that the “good character requirement knocks them out frequently from the possibility of citizenship”.

Recent figures obtained through a freedom of information request show 35 applications were rejected in 2017, while 59 and 39 child applications were rejected in 2016 and 2015 respectively. There was a peak in the number of rejections in 2013, when 78 child applicants had their request to register as British citizens denied.

Valdez-Symonds added: “The figures of those registering and those being refused simply leaves out the number of children who are not seeking to apply to register because they are being advised or being made aware that a simple caution or fine will mean they’ll be treated as not of good character.”

The good character requirement was introduced in 2006 and applies to applicants aged 10 or over who want to naturalise or register as a British citizen. Under current guidelines, an applicant may be rejected if they have received a fine within the last three years. If the fine is over three years old, applicants could still be rejected if they have received multiple fines that show “a pattern of offending”.

In 2012, the guidance was updated and young applicants were subject to the same guidance as adults. A 2017 review of the good character requirement by David Bolt, the independent chief inspector of borders and immigration, called on the Home Office to review the guidance and ensure it “makes explicit the scope for caseworkers to exercise discretion”. The government accepted the recommendations and noted: “Updated guidance will be published by the end of December [2017].” The Home Office is yet to publish this guidance.

In the meantime, children such as DB, a 16-year-old boy with special needs who was born and grew up in London, continue to struggle to gain citizenship. His guardian, SD, says he had been discouraged from applying once he was sent to the youth offending team (YOT) for 10 months in 2016. “I’ve been told it’s going to be difficult, it’s not going to be straightforward because of his criminal activity,” SD said, adding that social workers have told DB “he’ll struggle to get citizenship”.

Ronan Toal, an immigration and asylum barrister at Garden Court Chambers, said the application of the good character requirement was not consistent with juvenile justice. “It seems wrong, I think, if you have a principle that applies to juvenile justice, which is that you facilitate the child’s reintegration into the community after the child is committed an offence, whereas in nationality law, you exclude the child if the child has committed an offence,” he said.

Barratt echoes Toal’s point, adding there was “a dissonance” between the youth offending system, which focuses on rehabilitation, and the guidance around the good character requirement. “It’s in a child’s best interest to have a sense of belonging to the country where they’ve lived since they were very little and for which its their home,” she added.

A Home Office spokesperson said:“All citizenship applications are assessed on their individual merits.” The spokesperson noted that the good character requirement applied to all persons aged 10 and over, as that is the age of criminal responsibility, and added that revised guidance for the good character requirement would be published soon.