Border officials have been criticised after it emerged they target specific nationalities for deportation in order to fill up flights they have chartered. Activists said the practice led the government to remove people who still have active legal claims.

Documents seen by the Guardian show the Home Office team that manages the flights, and the team that picks up people suspected of living in the country illegally, work together to target people of a specific nationality if there is a flight due to go to their home country.

They target people already in immigration removal centres, as well as those living at home if necessary, to fill as many seats as possible, it is understood. In doing so, the government has deported many people who have applied for judicial review of their cases.

Volunteers with the Unity Centre, which works with those who are to be deported, said it had seen at least one case where a person claimed asylum the day before they were due to be removed. The person was subsequently deported without receiving any response to their claim, they said.

The volunteers added that at least one other person was deported despite having offered new evidence as to why they should stay. The evidence, they said, was never acknowledged by the government. And they cited other cases they had seen, in which people were removed while they tried to navigate the legal process via various means.

Changes to the rules, which allow the government to deport people then invite them to carry out their legal fight to return from outside the UK, mean the Home Office has the legal right to carry out deportations while some forms of appeal are ongoing, such as applications to bring judicial review.

But activists said this prevents many people from getting proper access to justice with “no real regard to the rights of the individuals involved”.

“The mentality of ‘deport now, appeal later’ means the Home Office can pretend that individuals will have the chance to pursue legal avenues of return. In reality this is a farce,” said Jasmine Sallis of the Unity Centre.

“These increasingly stringent rules result in families being split apart forever, children growing up without knowing their parents and individuals being torn unexpectedly from lives they have been living often for a very long time.”

Don Flynn, director of the Migrants Rights Network, said: “These are practices carried out by state authorities for reasons of minimising cost or administrative convenience.”

The hitherto unknown practice of targeting national groups was revealed in a document written by the former managers of Britain’s biggest immigration detention centre and released to the research group Corporate Watch under freedom of information laws.

Officials working for the government’s detainee escorting and population management unit, which manages the immigration estate, regularly charters flights based on its analysis of the countries to which there is the greatest need to deport people.

The documents show that the unit works in tandem with the Home Office’s immigration enforcement teams to select people to be placed on flights if they are liable to be deported to the countries to which they are going.

Corporate Watch fought a 10-month battle to force the government to hand over the information, finally getting a favourable judgment in June.

A meeting at Unity Centre, Glasgow, which supports asylum seekers and refugees. Photograph: Murdo MacLeod/The Guardian

Phil Miller, a researcher with the organisation, said: “It looks like the Home Office is rounding up groups of migrants from particular countries so it can fill a deportation flight, instead of removing people based on their individual immigration cases.”

The Home Office stressed that it did not remove anyone if it did not have the legal right to do so. “Those with no right to be in the UK should return home. We expect people to leave the country voluntarily but, where they do not, we will seek to enforce their departure,” said a spokesman.

He added: “Nobody is ever removed solely on the basis of their nationality. Every case is carefully considered on its individual merits and in full accordance with the law.

“Charter flights are generally used to remove people with a history of non-compliance or who pose a risk to the public, for their safety and that of other passengers. We always consider the availability of scheduled aircraft routes, the cost of maintaining detention and the individual circumstances of each case.”

The documents released to Corporate Watch also revealed that government-appointed contractors employed on performance-related pay deals have been allowed to assess their own work without checks being made routinely by Whitehall.

Two firms running immigration detention centres were required to fill out monthly self-audit reports volunteering instances in which they did not meet the government’s minimum standards. It is believed that the contractors faced a fine for each transgression.

The government later said it decides whether or not to carry out further checks into the audits on a case-by-case basis.

The approach was criticised by the campaign group Taxpayers’ Alliance, which said it was “absolutely nonsensical to leave an organisation with a vested interest in a clean audit to conduct the audit itself – the potential consequences are blindingly obvious”.

The group’s campaign director, Andy Silvester, said: “Officials all too often seem to think that by outsourcing a project or a service, responsibility and accountability are outsourced too. Failures at immigration centres can have awful consequences and the Home Office must step up its monitoring of the performance of these firms.”

The Home Office said: “Self-audit reports are part of a range of measures, including regular independent inspections, to ensure our contractors continue to provide safe and secure accommodation for detainees.

“The home secretary has commissioned Stephen Shaw to carry out a comprehensive review of our immigration detention estate to ensure the health and wellbeing of all detainees, some of whom may be vulnerable, is safeguarded at all times.”