An American woman who travelled to the UK to help her heavily pregnant daughter has claimed she was told to go back to the US by border officials at Heathrow on the grounds that her journey was not “essential”.

The 63-year-old woman, who had flown in from Washington DC on Monday, said she was reduced to tears by the hostile experience at passport control.

“I was so upset that I couldn’t help but start crying,” said Yoshie Rymar. “The agent told me to go to the ticketing counter to get a return ticket and go back to US. I couldn’t believe what I heard, and I didn’t know what to do.”

The Japanese-born American citizen had visited her daughter on numerous occasions before and did not expect to be rejected.

“When I got in the line at the passport control section, there was a very good-looking lady in front of me whose process was quick. So I expected the same way when my turn came. However, I was wearing a black-knit cap, glasses and a mask to protect myself. I was told to take those off because it was hard for us to communicate. He was irritated by my request to repeat his question.

“I explained how my daughter needed me because of her pregnancy and toddler. There was an agent next to him who was talking loud and my hearing was not so great, he was pretty irritated again. So he said to me, ‘How can you take care of your daughter if you can’t hear well?’ I thought it was a very harsh comment and I resented this rude remark.”

She was asked if she had been tested for coronavirus and was then refused entry. She was not given a reason other than the official making it clear her journey was “non-essential”, her daughter said.

Colin Yeo, an immigration barrister, said as far as he was aware there was no requirement in law to demonstrate a journey was essential before legal entry to the UK.

The only travel advice the government has issued relates to British citizens overseas, with an update following the virus outbreak advising UK nationals travelling abroad to return home.

“There has been no publicly announced change to the entry rules into the United Kingdom, as far as I am aware, and refusing a family member entry as a visitor because their travel is considered non-essential on the face of it looks unlawful,” Yeo said.

Rymar’s daughter, Rachel, who is married and lives in London, said her mother was left distraught at the airport.

“I don’t think I have ever heard her so upset. She was sobbing and I was too.

“She landed and phoned to say she was looking forward to seeing me and a half-hour later she called to say she was being sent back,” Rachel said. “She was not given any paperwork to sign or given any reasons in writing but was told it was not essential travel and she should go back to the BA desk and return to the US on the next flight.

“I am still upset. I am glad she’s back home and safe but it was a very bad day. Both of us were very distraught and now I’m scrambling round to try to put another plan in place,” she said.

“She was only going to stay here for a maximum of five months, well within the six months allowable – her return was for September.”

The case renews the question of what police and border authorities are legally entitled to do during the coronavirus crisis.

Two weeks ago the former supreme court justice Lord Sumption criticised Derbyshire police for stopping people exercising in the Peak District, saying such behaviour risked plunging Britain into a “police state”.

Rymar said she wanted to share her story to ensure that no one else suffered as she had, and to force the government to clarify what it meant by essential travel.

The Home Office confirmed that there were no extra restrictions because of the coronavirus on people entering the country lawfully and passengers were still being processed on the few flights into the country.

It said it could not comment on individual cases. “Our approach to tackling coronavirus is driven by the latest scientific and medical advice,” a spokesman said. “In line with that advice, Border Force officers continue to process arriving passengers in accordance with the immigration rules at ports across the UK.”