The Home Secretary will tell the Conservative Party conference that she will stop foreign offenders using the “right to a family life” to remain in Britain.
Her speech comes as a Liberal Democrat security expert backs Conservative criticisms over the Human Rights Act, saying it is preventing the deportation of extremists who could mount attacks during next year’s Olympic Games.
The Act, which incorporates into British law the European Convention on Human Rights (ECHR), is one of the flashpoints of the Coalition Government.
Critics, including Conservative ministers, say it is widely misused to help criminals and others escape justice, while Lib Dems insist it is misunderstood and should stay in place.
Article Eight of the convention, which ensures the right to a family life, has been cited by some foreign criminals fighting expulsion from Britain.
Scores have avoided deportation by claiming that because they have partners or children in the UK, being thrown out of the country would infringe their rights under Article Eight.
David Cameron, the Prime Minister, said on Tuesday, that the courts gave too much weight to the Article.
“The problem here is that there are foreign criminals in Britain, people sometimes actually who still threaten our country or could threaten our country,” he told BBC Breakfast.
“We are unable to deport them because they appeal to the courts under Article Eight of this charter, which is the right to a family life.
“We believe that the courts are currently giving too much attention to that rather than the protection of the UK.”
He added: “You are able to change the immigration rules and ask them to look more carefully about the danger these individuals pose.
“The right to a family life is not an inalienable right in the European convention so I believe this change will work. It is not the whole solution to the problem but it is a good start.”
Last year there were 102 successful appeals against deportation on human rights grounds which cited Article Eight.
Mrs May will announce today that immigration rules will be rewritten to set out explicit exemptions which would allow deportation regardless of family.
The new rules will direct the courts to give greater weight to sections of the ECHR which allow exceptions to be made.
Clause Two of the article permits exceptions that are “necessary in a democratic society in the interests of national security, public safety or the economic well-being of the country”.
Mrs May will say that the courts should consider that a range of factors outweigh a foreigner’s right to a family life.
Such factors will include criminal offences, breaches of immigration rules and relying on welfare benefits for income and housing.
Lord Carlile, a senior Lib Dem lawyer, today backs Conservative attacks on the controversial act, warning that it could allow some known extremists to remain in the UK.
In an article for the Policy Exchange think tank, Lord Carlile, a former government reviewer of terrorism laws, warns that the “promiscuous use” of Article Eight could put Britain’s security at risk by preventing the deportation of foreign terrorists now in jail.
He says there are more than 100 extremist offenders in custody, some of whom are to be released soon.
If allowed to stay in the country, he suggests, they could attack the 2012 London Olympics.
“This is not scaremongering. It is a realistic assessment of what we may face,” he says.
He also calls for changes to restrict the use of Article Three of the ECHR, which prohibits torture. Terrorists such as Siraj Yassin Abdullah Ali, jailed for helping in the 21/7 attacks in London, have used Article Three to remain in the UK.