A 21-year-old man who was born and raised in Britain has been told to leave the UK by the Home Office because he is not a British citizen.

Shane Ridge, a joiner from Colne in Lancashire who describes himself as “as British as they come”, received a letter from the Home Office last week informing him that his driving licence would be revoked as he had “no lawful basis to be in the UK”.

It came as a surprise because all of Ridge’s relatives are British citizens. His mother was born in Australia during a family holiday, but has lived in Britain since then and has dual citizenship.

Under UK law, if a child was born before July 2006, the father’s British nationality will usually only automatically pass to the child if he was married to the mother at the time of birth. Because Ridge’s parents never married, he does not have an automatic right to citizenship and is required to apply for “right of abode”.

Ridge said he did not know that his right to citizenship was not automatic, and is confused after being told he would have to leave his family behind or risk jail or a £5,000 fine for living illegally in the UK.

The letter said the Home Office was working with the DVLA, NHS and banks to “stop access to benefits and services for those with no lawful basis to be in the UK”. It added: “This includes you.”

Ridge was also told he must stop driving immediately.

“It’s surreal,” he said. “This is the only letter I have ever received in relation to me having to leave the country. It just came through my letterbox out of the blue.

“The last bit scared me the most – ‘leave the UK voluntarily’. I’m speechless – I don’t know what I can say. I received the letter from Immigration Enforcement saying they were going to revoke my driving licence and I should leave the UK voluntarily or face a £5,000 fine.

“I’m confused and worried that I’ll have to leave my entire family behind and move to a country that I don’t know. I don’t understand it because I was born in the UK. I did my GCSEs here, I’ve worked for six years, I pay tax and national insurance. Me and my girlfriend rented a house, I vote, I use the NHS and opened a bank account without any problems, ever.”

Ridge said he did not know he was not a British citizen until he received the letter.

He said he applied for a passport last year to go on holiday and his application was declined, but he then successfully applied for and holds an Australian passport. The Passport Office advised him that he would be able to travel and safely return to the UK after his holiday and since then, he said, he had had no indication of any problems.

“I applied for an Australian passport and was accepted because my mum was born there, despite both her parents being British, and therefore she has dual citizenship,” he said.

“I went to apply for right of abode myself after receiving this letter and was told by the Home Office that I need to apply for British citizenship first before I can do that.

“The laws on this have apparently changed in 2006 and they have changed backwards and forwards throughout the years. I just don’t understand how they’ve just got through to me now. I even have a birth certificate with my dad’s signature on it – he’s British.

“If I cannot get dual citizenship or right of abode, or if this isn’t a mistake, I don’t know what I’ll do.”

Ridge said he was particularly angry that his life as a law-abiding citizen in the country in which he was born had been thrown into doubt. “It’s terrifying. My parents keep telling me everything will be fine but I’m really scared.

“My girlfriend, Jodie, isn’t happy. Everyone is in shock and wondering how this can possibly happen. I’ve lived by the book – never had a criminal record.

“I have brothers and sisters. They have dual citizenship because my mum married their dad but my youngest sister, who is five, is also technically in the same position as me as my mum didn’t marry her dad.

“The letter even says they will stop me accessing the NHS or banks. I’ve always been to the doctors with no problems and me and my girlfriend have a joint bank account.”

The Home Office has not yet responded to a request for comment.