A British couple say they have been detained in the US after accidentally crossing the border from Canada.

The couple say they are being held in Pennsylvania with their three-month-old baby – which has left them “traumatised”.

They say were driving with relatives on 3 October when, to avoid an animal, they veered onto a small road.

A police officer then pulled them over, told them they were in the US state of Washington and arrested them.

The couple have detailed the “scariest experience of our entire lives” in a sworn statement that was provided to BBC News by their lawyer.

The family statement is the basis for a legal complaint lodged by their lawyer with the US Department of Homeland Security inspector general.

US immigration authorities confirmed to the BBC that the couple were being held, but denied their allegations of mistreatment.

Where were they taken?

The family’s attorney, Bridget Cambria, of Aldea – the People’s Justice Center, said the couple were driving in the Vancouver area on 3 October when they took a detour to avoid an animal on the road.

The family say they did not realise they had strayed over the US border.

They were pulled over by a police officer who did not read them their rights, nor allow them to “simply turn around” and go back to Canada, according to the complaint.

At first the young family say they were separated – with the husband, 30, being held in a male-only cell, and his 24-year-old wife and infant son in a women’s cell.

Later, the husband was taken to a detention centre in Tacoma, Washington, while his wife and their baby son were taken to a budget hotel near Seattle-Tacoma International Airport, according to the complaint.

The following morning they say they were driven to the airport, which raised their hopes that they were being flown back to Canada or the UK.

“But that was not the case,” the woman says in the sworn statement. Instead, they were flown to Pennsylvania – on the other side of the country.

They were taken on 5 October to Berks Family Residential Center (BFRC), one of three immigration detention centres in the US that can accommodate families.

The woman says: “We will be traumatised for the rest of our lives by what the United States government has done to us.”

US Immigration and Customs Enforcement (ICE) confirmed the family was in detention at the BFRC facility in Leesport, Pennsylvania.

A spokesman for the agency told the BBC that BFRC “provides a safe and humane environment for families as they go through the immigration process”.

“Reports of abuse or inhumane conditions at BFRC are unequivocally false,” he added.

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‘The worst experience’

The couple’s sworn statement says the cells are “frigid”, and staff have refused to turn the heating on until the end of next month.

“When I ask how I am supposed to keep my baby warm in this horrible cold, all they tell me is to put a hat on him,” the wife said in the statement.

“My baby can’t wear a hat all the time, he feels uncomfortable with hats and mittens and starts to cry.”

Staff, she added, confiscated her son’s formula for three days, as well as his teething powder, and would only provide “disgusting” blankets that smelt “like a dead dog”.

They say the baby’s skin is now rough and blotchy and he appears to have an eye infection.

“We have been treated like criminals here, stripped of our rights, and lied to,” she said. “It is not right.

“We have been treated unfairly from day one. It is undoubtedly the worst experience we have ever lived through.

“We have been traumatised and it has even damaged our relationship. No one should have to suffer this kind of treatment.”