The Home Office secretly acquired sensitive data, showing the nationality of people sleeping rough on the streets, in order to remove them from Britain, the Observer can reveal.

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A chain of emails sent by senior Home Office immigration officials show how they used information that was designed to protect rough sleepers to target vulnerable individuals for deportation. The internal correspondence shows the Home Office repeatedly requesting and finally gaining access to a map created by the Greater London Authority (GLA) that identified and categorised rough sleepers by nationality.

The secret arrangement meant frontline outreach workers tasked with helping the homeless by collating data for the GLA were inadvertently helping the Home Office to remove people who were from the EU or central eastern Europe. In May 2016, the Home Office introduced guidance enabling immigration enforcement teams to deport EU nationals, purely on the grounds that they were sleeping rough.

Human rights group Liberty said the Home Office’s behaviour demonstrated a “crisis of compassion” within the UK’s political system. It is making an official complaint to the European commission.

The Home Office actions are the latest example to emerge of the deliberate creation of a “hostile environment” for illegal immigrants by then home secretary Theresa May in 2013.

Sensitive information, such as the nationality, mental health and gender of rough sleepers, is collected by outreach workers and stored on a database called Chain – the Combined Homelessness and Information Network. This is used by many charities and agencies and was set up, according to the homelessness charity St Mungo’s, to support rough sleepers and help policymakers “identify emerging needs”.

The emails, revealed in FoI responses, show that the Home Office was given full access to the map for six months from September 2016, and that this was stopped only when homeless organisations found out and aired their concerns.

During this period, data indicates a marked increase in the deportation and forced return of EU nationals. In the final quarter of 2016, there was a 41% increase in the number of EU nationals detained, compared with the second quarter, when officials did not have access to the map. There was also a 42% increase in the number of central eastern European migrants detained. The number of enforced returns of EU citizens increased by 8%, with a 9% rise for central eastern Europeans.

Martha Spurrier, director of Liberty, said: “Vulnerable foreigners have been systematically targeted by a government obsessed with deportation, whatever the human cost. Children have been kept away from schools. Pregnant women and others in need of medical help are avoiding seeking it.

“Now even people forced to sleep on the streets will be frightened to seek support. Who knows where else the Home Office’s poisonous tentacles have reached? There is a crisis of compassion in our political system and it needs to be exposed and undone. The government must come clean and end these secret deals – or we will look to challenge them in court.”

The emails, most of them partially redacted internal correspondence between Home Office and GLA officials, show that the Home Office began attempting to get access to the data in May 2015. One email, dated 16 May 2015, shows a senior Home Office inspector asking GLA officials whether it is possible to “narrow down the locations” to either the postcode or name of a geographical hotspot on the map.

“We will use the maps in our authorities for deployment and briefings. Neither will be in the public domain but both would be susceptible to production on foot of a FoI request,” the Home Office immigration official writes. By November 2015 it appears to have made progress, with an email from a GLA senior officer providing “hotspot analysis” and information on how to track foreign nationals.

“We are trying to build in a timeline on the map so you can see where non-UK nationals have moved to over time, which hopefully will also be able to help you establish priorities by seeing patterns,” writes the officer.

Seven months later – on 6 June 2016 – an email sent to the Home Office suggests that the GLA and the mayor, Sadiq Khan, who was elected the previous month, are becoming concerned about the neutrality of the Chain database and the Home Office having access to such sensitive data. A Home Office response the same day refers to the usefulness of producing a heat map showing rough-sleeping hotspots and the deployment of Home Office immigration, compliance and enforcement (Ice) teams.

The GLA replies that it has provided the Home Office with information on central and eastern European nationals with an offer to provide “further breakdowns by nationality.”

Khan is now considering a new memorandum of understanding with the Home Office in an attempt to end homelessness in London, a development Liberty says is worrying given the exposure of the secret sharing of data.

A Home Office spokesperson said: “No one should come to the UK with the intention of sleeping rough, and those who are encountered doing this may be misusing their free movement rights. We work closely with councils and homelessness outreach services to ensure that those who are vulnerable receive the care they need, while supporting local authorities to tackle illegal immigration in their communities.”