The European commission is examining the increased detention and deportation of EU citizens from Britain and has warned it will take “appropriate action” against Theresa May’s government if it believes the rights of EU nationals are being compromised.

Detentions and enforced removals of EU citizens from the UK have risen sharply since the Brexit vote, prompting critics to claim the Home Office is deliberately targeting EU nationals as part of the “hostile environment” May promised for those she believes should not be in the country.

An email seen by the Observer, dated 5 September, reveals that the EU’s Brexit negotiating team referred a complaint relating to the detention of EU nationals in Britain to the commission’s directorate general for justice and consumers, whose remit is to ensure the EU “is an area of freedom, security and justice”.

A commission spokesman confirmed that the complaint was “being analysed”, and that action against the UK would follow if it was not complying with EU law.

Celia Clarke, director of the legal charity Bail for Immigration Detainees (BiD), said: “If other European countries were targeting British expats in this way, there would be justified outrage.”

During May’s Brexit speech in Florence last month, she offered to write legal protections for EU citizens living in Britain into the exit treaty. “The warm sentiments expressed in the prime minister’s Florence speech are at odds with the actions of Home Office officials, who appear to be riding roughshod over EU citizens’ rights to free movement,” said Clarke. “The government has a callous disregard for EU nationals’ rights to live and work in the UK.”

The development coincides with a significant increase in the number of EU nationals being deported since the Brexit vote, along with a spate of cases where EU citizens have been detained despite having committed no crime.

BiD said EU citizens were being detained and deported for relatively minor crimes, such as driving offences. The organisation also said that many EU nationals had been removed from the UK before they were able to mount a legal challenge.

Analysis of government data shows deportations of EU citizens are at their highest since records began, with 5,301 EU nationals removed during the year ending June 2017, an increase of 20% on the previous 12 months.

More broadly, the number of EU citizens detained has increased sixfold since 2009. Critics believe the figures corroborate claims that Brexit has in effect given the Home Office the green light to target Europeans in the UK.

Yet the email sent by the EU’s Brexit negotiating team, following a complaint by BiD over the detention and treatment of EU nationals, points out that Britain still has to fully comply with EU obligations. “EU law continues to apply to the full to the UK and in the UK until it is no longer a member,” officials state.

Meanwhile, European embassies have registered their disquiet over the Home Office’s seemingly hardline treatment of their citizens. The Slovakian embassy confirmed it had witnessed an increase in deportations of its citizens and felt that many were unjustified and callous. Ivan Zachar, head of the embassy’s consular section in London, said: “Many of those who contact us say they are not aware of a legitimate reason for their deportation: they have led an organised life in the UK, sometimes for many years, have been employed, paid taxes, and deny any wrongdoing that could have led to them being expelled.”

Zachar said some of the deportations also appeared unnecessarily abrupt. “We also have instances where the father of a family has been suddenly deported and the wife and children remain in the UK without sustainable livelihood support, with other financial commitments such as unpaid mortgage,” he said.

Among a flurry of recent cases reported to BiD is that of a 26-year-old Swedish national who had been living in the UK since he was 13 and was working legally. He committed two driving offences which led to a 36-week custodial sentence, and upon release from prison was detained and deported.

Another case involved an eastern European national who arrived in the UK in January 2015 and is due to be deportedon Monday. According to Clarke, the man and his wife were attacked in July by alleged associates of their landlord, who wanted them out of the house.

BiD’s client called the police but claims that, rather than pursuing the alleged attackers, officers took him to Colnbrook immigration removal centre in Harmondsworth, west London, where he has been ever since. He has committed no criminal offence in the UK and has worked throughout his stay.

EU directives make it clear that it is illegal for member states to expel EU citizens “except on serious grounds of public policy or public security”.

Other cases include two East European nationals currently held in Lincolnshire’s Morton Hall immigration centre with one, according to a BID legal official, detained on arrival from Ireland where he had been living and working while the other has “clear mental health problems.” Last week the same official met a Bulgarian with mental health problems who had been detained for three months despite having no criminal record.

An investigation is currently underway into the circumstances surrounding a 28-year-old Polish man who recently died after an attempt to kill himself at Harmondsworth detention centre in London.A Home Office spokesperson said: “We have toughened our response to foreign nationals who abuse our hospitality by committing crimes in the UK. In addition, those who are encountered sleeping rough may not have a right to reside in the UK and be liable for removal. No one should come to the UK with the intention of sleeping rough.”