The Government's fast-track appeal system for processing asylum applications has been formally quashed by the Court of Appeal.
Human rights campaigners said the controversial system has "finally been brought to a halt", but the Government is launching an urgent bid to have it reinstated.
Earlier this month, a High Court judge declared the system - used for a decade to speed up the processing of claims by asylum seekers kept in detention - "structurally unfair".
Mr Justice Nicol, sitting in London, had ordered the system to be quashed, but put a stay on his order taking effect to give the Lord Chancellor time to bring his appeal.
Today the stay was lifted at the request of Detention Action, the campaign group set up in 1993 to fight on behalf of individuals held in immigration detention.
Initially the Government opposed the move.
Lawyers for the Lord Chancellor agreed not to deport any applicants who lose fast-track cases pending the appeal, but argued the fast-track should continue to be used by tribunals, even though a judge had declared it unlawful.
Neil Garnham QC said the Government was "betting" on winning its appeal.
But the QC withdrew his opposition to the system being quashed with immediate effect after Lord Justice Sullivan, sitting with Lady Justice Gloster and Lord Justice Floyd, suggested that "it might be undesirable from the point of view of the justice system" if tribunals were to make decisions using a system found to be structurally unfair.
The judge said it could be weeks before the Government appeal is decided and that could lead to hundreds of cases having to be reheard if the appeal court dismisses the appeal.
Following a short adjournment, Mr Garnham dropped his opposition to the stay being lifted.
Detention Action reacted by saying: "The Court of Appeal has today finally brought to a halt the detained fast-track appeals process."
Detention Action director Jerome Phelps said: "We are delighted that asylum-seekers will no longer face a detained appeals process that is so unfair as to be unlawful.
"It is unfortunate that it has taken so many court rulings to finally suspend this deeply flawed process.
"People seeking protection from war and persecution deserve better from British justice. We hope that the Government will take this opportunity to reflect and develop a different approach that is fair."
Refugee Council chief executive Maurice Wren said: "This ruling is a very welcome, though painfully long overdue, recognition that the detained fast track is a dangerous caricature of justice.
"Today the courts have acknowledged the unlawfulness of a system that for administrative and political convenience undermines justice and puts lives at risk."