Dozens of staff at the Byron Hamburgers chain of restaurants have been arrested in an immigration swoop, it has emerged.

The Home Office has confirmed 35 nationals from Brazil, Nepal, Egypt and Albania were among those rounded up in the raid, which took place across London on the morning of 4 July.

A senior worker in one of the branches alleged that staff had been told to attend a health and safety meeting at 9.30am that day but immigration officials quickly arrived and started to interview people.

“It is fucking disgusting. Some of these people worked here for four or five years and they weren’t even given a chance to say goodbye,” said the worker who spoke on condition of anonymity.

A source at the Home Office said that reports that up to 80 staff had been deported were wide of the mark, confirming that 35 people were arrested on suspicion of breaches of immigration laws.

“They were arrested in order to progress potential immigration offences,” the source said.

Byron confirmed it facilitated the raid at the Home Office’s request but refused to respond to claims that it set up staff meetings on the false pretence they were for health and safety training.

It said: “We can confirm that several of Byron’s London restaurants were visited by representatives of the Home Office. These visits resulted in the removal of members of staff who are suspected by the Home Office of not having the right to work in the UK, and of possessing fraudulent personal and right to work documentation that is in breach of immigration and employment regulation.”

It said that the Home Office acknowledged that it had complied with its legal responsibilities as an employer but it had been shown “false/counterfeit documentation” by those at the centre of the alleged immigration breaches.

“We have cooperated fully and acted upon the Home Office’s requests throughout the course of the investigations leading to this action, and will continue to do so.”

Byron, which has 56 restaurants across the country, is owned by investment firm Hutton Collins which bought the chain in a £100m deal in 2013.

Reports of the raid first appeared in a Spanish language online newspaper, El Iberico, in London and quickly spread across social media, prompting plans of protests and boycotts of the restaurant.

Amelia Womack, the deputy leader of the Green party, said: “These reports are deeply shocking. If these accusations are true than the bosses at Byron should be utterly ashamed of themselves for turning people’s lives upside down.”

She said: “People who are settled and working in the UK should be able to apply for residency so as to continue contributing to our society and our economy.”

A Home Office spokesperson said: “Immigration enforcement officers carried out intelligence-led visits to a number of Byron restaurants across London on 4 July, arresting 35 people for immigration offences. The operation was carried out with the full co-operation of the business.”