A talented 17-year-old violinist living on the frontline in south-east Ukraine has been left waiting three months for a British visa, revealing serious flaws in government promises to help unaccompanied children.

Anastasiia, who lives in the Russian occupied Zaporizhzhia region, where fighting has been intense, has faced constant shelling while waiting to join a family in Hertfordshire.

“There are so many bombs and rockets and buildings on fire now,” she said. “They are fighting every day. I can go out but it is also very dangerous.”

The Guardian is not publishing her surname as she will need to cross checkpoints to escape.

Anastasiia is one of about 1,000 unaccompanied children who applied to Britain under the Homes for Ukraine scheme and were left in limbo after the government changed its policy and said children had to travel with parents or guardians.

The issue was supposed to have been resolved last month after the government announced that it would allow a safe passage to the UK for those who had already applied.

But small print in the policy reveals that most will not be eligible as it says lone children should already have known their hosts before war broke out, unless in “exceptional” circumstances.

A letter sent at the end of June informed Anastasiia that in “early July” she would be contacted about a new scheme but that her hosts would normally only be eligible if they knew her before the outbreak of war. She has heard nothing since.

Anastasiia is one of several young musicians helped to join musical British families after a push from the music trade body, the BPI. While those who were over 18 were able to come to Britain, Anastasiia was left waiting.

She said she had “dreamed of being in a big orchestra” since she was young and that the “massive destruction” of her home town meant her dream would be hard to realise unless she left.

Sally Belsham, 57, from Bishops Stortford in Hertfordshire, has musical teenagers of her own, and has been ready to welcome Anastasiia since their application on 11 April.

“Just leaving her in this situation is horrible,” she said. “It’s really inhuman. I understand the need for safeguarding but you cannot have a system that leaves people in limbo like this.”

Both Belsham and her husband, Giampaolo Martinelli, 54, have extensive background checks as she works with refugees and Martinelli is a cardiac anaesthetist. They have 17-year-old triplets and a 19-year-old son at university.

Belsham added: “There is still no certainty that she will even be approved under this scheme, because we didn’t know her before the war.

“It’s a nonsense, really. Clearly, the reason we’re in this situation is because of the war and our desire to help and her need to get out.”

Anastasiia’s parents, who look after four adopted children with health needs and cannot leave, do not want her to go without the visa. Without the certainty of a host family, they worry about her travelling elsewhere in Europe alone.

Before the war, Anastasiia attended music school and practised for five or six hours a day. Now she says she struggles to, because she is often sheltering in the basement of their home and helping to care for her adopted siblings.

“I thought it would be great to practise in the basement but the kids have lots of energy and I always need to help my parents,” she said.

The Labour peer Alf Dubs said it was “absolutely shocking” that teenagers were being left at the frontline for months on end. “When young people are living in a war zone, more time is more danger,” he said.

He also criticised the loophole in the scheme, saying it was “yet another attempt” to restrict the number of unaccompanied children coming from Ukraine. “How would anybody have known a sponsor in this country before the conflict started?”

A Department for Levelling Up, Housing and Communities spokesperson said: “We have a responsibility to keep children safe and we have put in place strong safeguarding measures to protect them once they arrive in the UK.

“The sponsor should, wherever possible, be personally known to the parents. However, local authorities will review cases and can choose to make exceptions.”