Dozens of Nigerian care workers have been arrested in immigration raids across London and are being held at various removal centres.

They have been told they will be forcibly removed from the UK on a charter flight on Tuesday.

The care worker were arrested for allegedly overstaying their visas. Some had worked for more than a decade and say they are distraught at the prospect of leaving behind many elderly and vulnerable people they have forged close bonds with.

Some of those being held were working for a large company called Mears Group, which provides staff to care for elderly and disabled people.

The Home Office confirmed that on 7 and 8 Septemberimmigration enforcement officers conducted simultaneous raids at residential addresses across London. Thirty-four care workers were arrested and detained while another 21 were served with immigration documents and placed on temporary release.

A Home Office spokesman said: “This intelligence-led operation was conducted in response to allegations that foreign nationals have been using forged documentation to gain employment illegally as carers.”

Many of the detained workers are being held in Yarl’s Wood immigration removal centre in Bedfordshire. One said: “We are getting all kinds of phonecalls and messages from the people we have been looking after for many years asking us what has happened to us and when we are going to go back to look after them. We know our clients so well – how they like their cups of tea, what their favourite clothes are. But now we’ve lost our clients and our clients have lost us.”

Olusoji Bolarinwa, 37, is one of the Nigerian care workers who is being detained at Morton Hall immigration removal centre in Lincoln. He received a Dignity In Care award in 2013 and has been nominated for the same honour this year.

“We heard that up to 130 people were targeted in night-time raids earlier this month,” said Bolarinwa.

“I was not at home when I was arrested. I was at a friend’s house. They had not come looking for me, they came for my friend but when they found me at his house they arrested me too. These raids were terrible.

“They were banging on the doors in the early hours of the morning. The people we were looking after keep asking where we are and when we are coming back. I think they are being told that we are off sick, but if we are deported on Tuesday the ‘sickness’ will not end.”

A female care worker said that she was woken up in the early hours of the morning by battering on her door. “I thought there was a fire,” she said. “It is true that I had overstayed my visa but many of us have worked as carers for years and years, some for more than 10 years. In that time we have always paid our taxes, our national insurance and our pension contributions and have had all the police checks.

“Why did nobody raise the issue of our visas before now? I loved my job, I was providing personal care to old people. We were being paid peanuts but we didn’t mind because at least we had a roof over our heads and could send some money back to our families in Nigeria. Many carers have overstayed their visas. If the Home Office remove us all there are not going to be enough people to look after all the old and vulnerable people in this county.”

One elderly client told the Guardian: “I miss her, she really knows me well and cares about me,... I didn’t understand at first why she went away without telling me. Other carers have come but I keep having to tell them what to do and it’s confusing.”

Alan Long, one of the directors of Mears Group, said not all the carers picked up by the Home Office had worked for the firm. He added: “We have got very good procedures but one or two do tend to slip through the net. It’s unfortunate that some of the staff were long-term workers with us. We always work with the Home Office and I don’t think that this has impacted on our service.”

Mears Care in Hounslow received a glowing report from the Care Quality Commission this year scoring “good” on all five key indicators. The CQC found that older people and those with physical and mental health problems who were receiving care reported their carers to be kind, polite and considerate and said they felt supported by them.

Sally Warren, deputy chief inspector of adult social care at the CQC, said: “Our priority is to make sure that Mears Care Hounslow continues to provide people with care and support that is of the standard that they deserve and that we expect. We are continuing to liaise with Mears Care to monitor the impact that the staff vacancies are having on the quality of care and will be kept informed on their recruitment and mitigation plans.”