A Syrian teenager left suicidal after the Home Office failed to respond to his application to join his family in Britain is finally set to be reunited with his loved ones.

On Thursday, after the Guardian contacted the Home Office, Moustafa’s lawyers were told that his case had been approved and he would be brought to the UK from Athens, where he has been living for a year, as soon as possible.

The Home Office said in a statement to the Guardian: “When processing applications, we ensure that the best interests of unaccompanied children are fully considered.

“We apologise for the delay in processing [Moustafa]’s application and any distress this has caused him. [His] case is being considered as a matter of urgency.”

Speaking from the north of England, Amira (not her real name), Moustafa’s aunt, said: “I have no words for my happiness.

“Mentally he has been suicidal, devastated. Twice I spoke to him and he said he was going to kill himself.”

Moustafa (not his real name), who travelled to Greece last summer from the Syrian city of Deraa aged 16, had waited since January for a reply to his application.

Under an EU law known as the Dublin regulation, unaccompanied minors have the right to apply for asylum in any European country where they have a close relative.

Moustafa spent his first few weeks in Athens sleeping rough before a charity helped him into one of the oversubscribed accommodation centres.

Speaking to the Guardian from his lawyers’ offices, Moustafa said he had been desperately unhappy in the Greek capital.

“At first I hid in gardens, where nobody could see me, or under the table at cafes. I was very scared. I would rather die, I think, than carry on waiting.”

He said the first weeks were the worst. “I just tried to go and sleep where nobody could see me, I was very scared.

“Deraa, where I am from, is destroyed. My mother and sister and brother are there now and I am so worried about them. I thought I could go to my aunt and uncle.”

Ella Dodd, a British lawyer working with Refugee Legal Support who has been supporting Moustafa since last October, voiced concerns over the “unprecedented” delay.

Dodd said: “He has been very upset. I have been in constant contact with him and he has been sending me WhatsApp messages that say: ‘I don’t know if I can carry on.’”

Dodd said delays in allowing children to join family members are widespread. “The Dublin regulations are not being applied with good faith. Long delays are routine and teenagers find it difficult to understand the wait. We have children go missing while we wait because the delay is so long.”

Annette Elder of Elder Rahimi solicitors, who represented Moustafa in the UK, said he was one of many children facing long delays in joining family in the UK.

“This case is not alone,” said Elder. “Progress in getting the Home Office to do their job is dependent on having family members who have the time, ability and resources to be able to instruct lawyers in the UK.

“And it depends on the young person having access to representation in the country where they are located, who can work with lawyers in the UK. Having all this in place is not at all usual.”

In March, the Guardian reported that children who spent up to a year in Calais waiting to join family in the UK went on hunger strike. In at least one case, a child attempted suicide.

Figures from May show that there were nearly 4,000 unaccompanied migrant children living in Greece, and just over 2,000 places in safe accommodation. Another thousand are believed to be living in squats or sharing unsafe housing arrangements, leaving a thousand more on the streets.

The charity Safe Passage estimates that at least half of unaccompanied children in Greece could have family members in another EU country, although lack of official data makes it difficult to get a clear picture.

Eleanor Harrison, CEO of Safe Passage, said: “[Our] research has found children routinely waiting 16 months to reunite with family in another member state. Unfortunately, the UK is one of a number of countries failing to meet its obligations to child refugees. As this case highlights, the impact on the physical and mental health of children who are denied swift family reunion can be severe.”

Boris Cheshirkov, a spokesman for the UN refugee agency in Greece, said children were in danger there and European governments needed to act.

“We are concerned for the welfare of unaccompanied children, hundreds of whom are sleeping on city streets or living in unacceptable and unsafe accommodation,” said Cheshirkov. “ [This] puts them at risk of exploitation, abuse, crime, trafficking and mental harm.

“[We urge] other countries in Europe to shoulder the responsibility by speeding up family reunifications and opening up relocation places. The UK’s Dubs scheme is such a programme. More than 75 children have been submitted and 43 children have been relocated under this scheme. We hope [Dubs] will set a precedent for other European countries to open their doors to the most vulnerable.”