The fast-track deportation of foreign nationals refused permission to remain in the UK has been declared unlawful by the High Court.
A judge ruled that the Home Office policy meant people were being given “little or no notice” of removal and were deprived of access to justice.
The policy was challenged by Medical Justice, which provides medical and legal advice to people facing removal.
The Home Office said it was “disappointed” and would appeal.
Medical Justice and the Home Office each laid out their case at a hearing last month, and on Monday Mr Justice Silber ruled that the fast-track policy was “unlawful and must be quashed”.
He said those subject to a removal order must have the right to challenge it, but fast-tracking meant it was often not possible to obtain sufficient legal advice in time.
But an “exceptions policy”, introduced in March 2007 and widened in January this year, led to some removals happening much faster.
At last month’s hearing, Dinah Rose QC, appearing for Medical Justice, said that in some instances immigration officers arrived late at night to escort people to flights leaving only a few hours later.
Home Office lawyers argued that the deportation policy was “sufficiently flexible” to avoid any human rights breaches, and that detainees were given as much notice as possible before removal.
But BBC home affairs correspondent June Kelly said the court felt the government had failed to bring in adequate safeguards to ensure those deported at very short notice were not put at risk.
Medical Justice was represented in court by legal charity, the Public Law Project (PLP). Diane Astin, from PLP, said Monday’s ruling was “tremendous”.
She said it was of particular legal significance because the judge spelt out clearly what constituted access to justice and what could be an impediment to it, such as the availability of crucial documents.
But a Home Office spokesman said: “The policy of making limited exceptions in special circumstances to 72-hour notification of immigration removal has been an important element of our management of removals.
“The government remains committed to removing individuals with no right to be in the UK as quickly as possible.”
Fast-track deportation was introduced to deal with certain types of case, such as those involving unaccompanied children who could not be detained before removal and posed a risk of absconding.
It was also applied to individuals thought to be at risk of suicide once given their removal instructions, and instances where reduced notice was deemed necessary “to maintain order and discipline” at a detention centre.
Welcoming the ruling, Donna Covey, chief executive of the Refugee Council, said many people refused asylum in the UK “have serious grounds for appeal if given the chance”.