An investigation has uncovered scores of cases where offenders from overseas, including killers and sex attackers, have been able to stay in Britain despite strenuous attempts by the Government to deport them.

The findings demonstrate how criminals are using the 1998 Human Rights Act to avoid being sent back to their homelands – despite a pledge by Gordon Brown to remove any foreigner who breaks the law.

In cases thought to have cost the taxpayer hundreds of thousands of pounds, immigration judges have overturned attempts by the Home Office to remove at least 50 foreign criminals from the country in the past 12 months, after lawyers argued that deporting them would breach their human rights.

In July 2007, shortly after becoming prime minister, Mr Brown told foreign nationals to “play by the rules or face the consequences”, warning: “If you commit a crime you will be deported from our country.”

Yet in several cases, criminals were allowed to remain in the UK despite courts acknowledging that they pose a danger to the public.

Foreign offenders who have won the right to stay in Britain include:

:: Mark Cadle from Belize, jailed for having sex with a 14-year-old girl, who judges said would have his human rights infringed if deported because his family live in Britain.

:: Rohail Spall, a Pakistani businessman man jailed for attempting to spike a woman’s drink so he could rape her, but allowed to stay because deporting him would breach his right to family life.

:: A Pakistani man in his forties who indecently assaulted a friend’s six-year-old daughter at a cinema. He was jailed for two years, but on release was allowed to remain in the UK on family grounds. He arrived in Britain as an adult but has several children who were born here.

:: A Somali with convictions including manslaughter and robbery, who the court said would be “at serious risk of persecution” if returned because he is from a minority clan.

The 50 cases, which were all rigorously opposed by the Home Office in court, include 15 criminals with convictions for violent crime, four sex offenders and 13 with drug convictions.

The total is likely to represent only the tip of the iceberg because they were all heard at the second tier of appeal, and many more criminals could have won the right to remain here at the lower level. Official figures are not available, according to the Home Office and the courts.

In most of the cases, lawyers argued that deporting the criminals would breach their right to a family life under the Human Rights Act, because they have children or other relatives in this country. In other cases, courts found that they would be in danger if deported.

The Act, which became law during Tony Blair’s first term as prime minister, incorporates into domestic law a European treaty signed in 1950.

Chris Grayling, the shadow home secretary, said: “If you come to Britain and commit a serious offence you should expect to be deported, full stop.”

The Conservatives have pledged to repeal the Human Rights Act and replace it with a new Bill of Rights.

Simon Reed, vice-chairman of the Police Federation, said: “What do these individuals have to do to be deported from this country?

“Most fair-minded people will be dismayed that the tribunals make such decisions. They should consider the human rights of the general population and not of a few criminals individuals.

“The police, immigration service and the Home Office work hard to identify these people, and clearly the courts are out of step with reality. We have enough criminals of our own – we do not need additional offenders thrust upon us by the courts.”

One of the most disturbing cases uncovered by this newspaper is that of Cadle, 42, originally from Belize, who was sentenced to three years and four months’ imprisonment for having sex with a 14-year-old girl. He infected her with a sexually-transmitted disease.

Cadle, who lives in Norwich and came to the UK at the age of 18, had a string of other convictions including racially-aggravated assault.

The appeal judges noted that according to lawyers for the Home Secretary, Cadle was a “significant danger to the public” and: “It was considered that there was a likelihood … of the appellant reoffending in the United Kingdom were he not to be deported.”

Yet Cadle’s lawyers persuaded the immigration tribunal that it would breach his human rights to split him from other family members. He has five children by five different mothers, and his mother and half-siblings live in Britain.

Spall, 42, from Pakistan, was caught dropping a sedative into a woman’s drink so that he could rape her. Police found a blister pack of the drug Xanax – a weaker version of date rape drug Rohypnol – in his pocket, and hundreds more in the boot of his chauffeur-driven Mercedes.

He was sentenced to three years and six months in prison after the original two-year sentence was increased following a public outcry.

Yet in October last year Spall successfully argued that removing him would breach his right to a family life, because his wife and four children are settled in Ilford, east London.

Beris Simpson, 56, a reggae musician who arrived in Britain from Jamaica in 1982, has several convictions for violent crimes including causing grievous bodily harm, and drugs offences.

In 2004, a court ordered him to hand over £29,000 after convicting him of possession of drugs with intent to supply.

Simpson, who records under the name “Prince Hammer” and has toured with bands including The Clash and UB40, has five children by two mothers. The court ruled that because the youngest have no links with Jamaica he should be allowed to remain in Britain.

In another case, a Congolese national, who came to Britain aged five or six, last month defeated the Home Office’s attempts to deport him even though the appeal judges noted: “The appellant was regarded as very dangerous when convicted (up to and including possible rape and murder). He remains at moderate risk of future violent offending.”

The tribunal described the 25-year-old as “a long-time user of crack cocaine, a burglar on an industrial scale and a convicted sex offender”.

During a burglary in 2000 he discovered a young woman asleep, sexually assaulted her and beat her unconscious when she protested. He was jailed for five years.

Despite his long history of serious crimes, immigration judges concluded that the man should not be deported to the Democratic Republic of Congo, a country which they described as “a very difficult and dangerous environment”.

In their ruling on the case, which took more than five years to resolve, the judges added: “However unattractive his behaviour may be, the appellant is a ‘home-grown’ criminal who has grown up in the United Kingdom and cannot properly now be said to belong anywhere else.”

In another case, a Jamaican gangster was convicted of attempted murder after he fired a shotgun at close range at a man, blinding him in one eye. He was jailed for 12 years and recommended for deportation by the judge.

But the Asylum and Immigration Tribunal (AIT) decided in February that it would breach his human rights to send him back to Jamaica on the completion of his sentence, because his life may be put at risk and he may face “torture or inhuman or degrading treatment”. He said he feared retribution after a feud between two branches of his family led to one of his relatives being shot dead.

Several foreign nationals convicted of robbery have defeated deportation moves, including a man from the Democratic Republic of Congo who was handed a five-year jail term for what the trial judge described as a “particularly nasty” robbery of a shopkeeper involving two accomplices, a 10-inch knife and stun guns.

The offender, who arrived in Britain in 1993 when he was aged nine or 10, escaped deportation because Article 8 of the European Convention on Human Rights, enshrined in UK law under the Human Rights Act, requires “respect for private and family life”.

At least two foreigners convicted of causing death by dangerous driving have successfully challenged deportation moves. One, a Turkish man who entered Britain illegally in the late 1990s with his family when he was aged 12, was convicted of causing death by dangerous driving in June 2007 and sentenced to two years and eight months in jail. At an immigration tribunal appeal in August, his lawyers persuaded judges that, under Article 8, it would be “disproportionate” to deport him.

The issue of foreign criminals came to prominence at Westminster in 2005 when Charles Clarke was sacked as home secretary after it emerged that more than 1,000 overseas offenders had been released from prison without being considered for deportation.

Lin Homer, chief executive of the UK Border Agency, said: “We have made it clear that we will not tolerate those that come here and break our laws, and last year we deported a record 5,400 foreign criminals.

“The UK Border Agency vigorously opposes any appeal against detention or deportation but if the courts insist a detainee should be released and cannot be removed we have to accept their judgment.”

She added: “The system for dealing with the consideration and removal of foreign national prisoners is robust, with all foreign national prisoners considered for deportation before release.

“Over the past three years we have improved the way we work with the Prison Service to ensure that in the majority of cases we are able to remove foreign national prisoners before they complete their prison sentence, and around a quarter go before the end of their sentence.”