The number of EU nationals detained in immigration centres has increased fivefold since the Conservatives came to power, The Independent can reveal.

The sharp rise has led to concerns the Government is trying to “spread anxiety” among people from EU countries living in the UK, in an effort to deter others from moving to Britain.

In 2015, the last full year for which Home Office data is available, 3,699 EU citizens were detained under immigration powers – 11.4 per cent of all detainees – while in 2009 just 768 were detained, 2.7 per cent of the total.

In many cases, no crime had been committed, with people detained for reasons such as losing their ID card or having a birthday party in a park, according to the charity Bail for Immigration Detainees (BID).

Barrister Adrian Berry told The Independent he believed the Government was pursuing a policy of deliberate hostility towards EU citizens, which could intensify when the country leaves the EU.

“The policy of the Home Office towards EU citizens started on Theresa May’s watch as Home Secretary, before the Brexit referendum,” he said.

“It’s a marker of her approach to EU citizens and it’s one we should all take very seriously when we look to her promises on and after Brexit.”

The detention of EU citizens has continued to shoot up, with 1,227 detained in the third quarter of 2016 – 17 per cent of the total number recorded in that period.

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Since 2010, when Ms May became Home Secretary, the number of EU nationals expelled from Britain has risen by 256 per cent. “Removing some people is also telling other people that their status is insecure. It functions to spread anxiety,” said Mr Berry.

“They have this policy of removing EU citizens when it’s unnecessary. If you’ve committed a serious criminal offence, you could be liable for deportation and banned from re-entry. [But] this is a lesser technique called administrative removal, where you’ve committed no crime but they’ve just decided that you’re not doing anything like working or being a student.

“These are not criminals. No one cares about a French person in Kensington not doing anything. They just pick on the lower-income people from Eastern Europe.”

In her speech outlining the Government’s Brexit plans, Ms May said she wanted to “guarantee the rights of EU citizens who are already living in Britain, and the rights of British nationals in other member states, as early as we can”.

But John Hopgood, BID’s Policy and Research Manager, said the Prime Minister’s words were hard to swallow as there had been “very mixed messaging” from Government over the rights of the some three million EU citizens settled in the UK.

“I can’t see how it can’t get worse after Brexit,” he told The Independent. “It’s a real worry for a lot of people. They don’t know what they need to do to have the right to stay here afterwards… There’s no guarantee they will have that sort of security when they leave the EU.”

One Polish national, working in the UK with the right to be in the country, was detained after officials apprehended him in a public park while having birthday drinks, according to BID.

The Home Office told him they planned to expel him for “abusing his EU law rights”, said the charity, and he remained in detention for five months despite there being an injunction stopping his removal.

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“An increasing number of EU nationals are being detained, who are facing removal from the UK over, in general, pretty much nothing,” said Mr Hopgood.

“By and large they’re there picked up on for far less serious things that if they were from outside the EU that wouldn’t qualify them for removal or deportation at all.”

“It seems to have happened very recently, very dramatically, this increase, and it’s almost without warning. There’s been no Government announcement on ‘we’re going to be tougher on [EU] immigrants’,” he said.

BID also said they had helped an Italian national who was held in detention for eight months because he had lost his Italian ID card, despite co-operating with the Government efforts to return him to Italy.

Mr Berry said in certain cases the Home Office has had to pay out “huge damages” for unlawful detention of EU citizens who were acting within their rights.

In a blog post, he cited an example taken to the High Court in which the Home Office had attempted to remove a Polish national who was stopped by police while sleeping rough.

The man was detained for more than five months and prohibited from working when he was temporarily released, despite saying they wanted to remove him as a person neither working nor seeking work.

The High Court ruled his detention unlawful and he was awarded damages, according to Mr Berry.

Campaigners have urged Ms May to end the uncertainty affecting EU citizens in the UK by guaranteeing their right to remain in the country after Brexit.

A joint statement issued by the3million – which campaigns to preserve the rights of British citizens in Europe and Europeans in the UK after Brexit – and several migrants' rights groups called for a guarantee to be made before Article 50 is triggered.

A Home Office spokesperson said: "The general public expect robust action to be taken against foreign national offenders who pose a risk to the UK – and that’s why we deport those who abuse our hospitality by committing crime."