An investigation into decisions by the country's highest immigration court has revealed how some judges rule far more often than others in favour of offenders seeking to avoid deportation.
While one judge backed claims by 11 criminals and ruled against only two, another ruled against all nine criminals whose cases he heard.
Among cases heard by the three judges who allowed the most appeals - Richard McKee, Kate Eshun and Jonathan Perkins - one saw a man permitted to stay in Britain after serving a nine-year sentence for manslaughter.
The killer won his case in front of Miss Eshun, partly because of his right to a "family life" with his brother who was also jailed for the same killing.
Others among the 26 allowed to stay in the country included a man who punched an 84-year-old Alzheimer's sufferer in the face, and a motorist who killed a woman while driving at 60mph in a built-up area.
The findings indicate that plans by Theresa May, the Home Secretary, to crack down on the way foreign criminals use human rights to avoid being deported risk being undermined in the courts.
MPs will this week be asked to back the new proposals, which will see judges issued with new guidelines saying that only in "exceptional" cases should criminals be able to avoid deportation by citing their "right to a private and family life" under Article 8 of the European Convention on Human Rights.
But lawyers claim the Home Secretary's plans lack teeth and will result in a cascade of legal challenges and delays.
The investigation looked at all 184 appeals against deportation by foreign criminals in the 12 months up to June 1 which were brought under Article 8, in whole or in part, in the Upper Tribunal of the Immigration and Asylum Chamber.
It showed that in these cases - which are exactly the kind Mrs May is seeking to curb - criminals won 96, or just over half.
However, there was a startling variation in the "hit rate" under different judges.
The analysis showed Mr McKee, 64, a senior immigration judge, heard 13 cases between June last year and last month. In 11 he ruled in favour of the criminal bringing the appeal, with just two going in the Home Office's favour.
Those he allowed to stay in Britain included:
* Wabi Longange, from the Democratic Republic of Congo, a failed asylum seeker who caused the death by careless driving of a woman passenger.
* An Australian man, identified only by the initials CB, who sexually assaulted a 17-year-old girl for whom he had been a foster carer since she was nine or 10.
* Amar Chennaoui, 43, an Algerian, who was jailed for two and a half years for unlawful wounding.
Miss Eshun, another senior immigration judge, heard 13 cases during the period, in which she ruled in the criminal's favour nine times - including two on the grounds that they were European Union citizens - and in the Home Office's favour four times.
Criminals she let stay in Britain included:
* Nuno Jesus Ramos, 26, a Portugese national who the Home Office tried to deport for his role in the manslaughter of 47-year-old Joao DaCosta Mitendele, who was robbed in his own home, tortured and left to suffocate.
* A Mauritian man, Peter Derek Anil Gokhool, 41, who was given a hospital order after he admitted assaulting an 84-year-old Alzheimer's sufferer, whom he punched twice in the face after encountering him in the street.
* Mohammad Farooq Khan, from Pakistan, who had been convicted of 71 offences over 28 years, including drug possession and racially or religiously aggravated harassment. The judge upheld his "family life" claim even though he lived with his brother and not with his wife and children.
Mr Perkins heard seven Article 8 claims by foreign criminals in the same period, and rejected the appeal by the offender in just one case.
In stark comparison, Lance Waumsley heard nine cases and in all of them he rejected the criminal's case and upheld the Home Office's original decision that they should be deported.
Another judge, Andrew Jordan, ruled in the Home Office's favour seven times, and upheld just one criminal's Article 8 claim.
In other Article 8 cases allowed by judges over the period included Taoufik Didi, a Moroccan drug dealer who claimed his right to family life despite being a bigamist; Johnathan Bartley Stables, an American fraudster; and Gary Ellis, a Jamaican drug dealer who made two successful claims under the human rights law.
The Judicial Communications Office declined to say what experience each judge had prior to joining the Upper Tribunal.
Mr McKee, a Cambridge graduate, worked for the Immigration Advisory Service as a barrister in the 1990s, bringing appeals for immigrants and asylum-seekers. He began to adjudicate on immigration cases in 2000.
Mr Perkins, a graduate of Cardiff University, has heard immigration appeals since 1993 and is a Methodist lay preacher.
One of the appeals which he allowed was that of Lionel Noel Hibbert, who had three children by three different women almost simultaneously in 2001, and later claimed the right to family life.
Mrs May published proposals to restrict the use of Article 8 in deportation appeals last week.
Sean Mcloughlin, an immigration specialist at TRP Solicitors, said: "I think it is going to be a potentially futile exercise by the Government. I don't think it is going to achieve what they want to achieve.
"They are stating what their interpretation of the law is, but interpreting the law is the judges' job. They are in for a big battle and I think they are going to lose.
"The proposals will lead to a lot of legal challenges and therefore a fair amount of expense. There will be an increase in applications for judicial review, applications to the Court of Appeal, the Supreme Court and ultimately to the European Court.
"Of course, the court at Strasbourg already has a large backlog, so that is potentially where it will all go pear-shaped."
MPs are due to debate the new rules and guidance to judges on Tuesday.
A spokesman for the Judicial Office said: "Judges make a decision in each case according to the evidence before them.
"They apply the law and the developing jurisprudence binding on them at the time of the case. Where either party is aggrieved with a decision of the Upper Tribunal there is a right of appeal."