In a written answer in the House of Commons, he said: 'I have concluded, however, that there are difficulties both of principle and practice in bringing this type of behaviour within the scope of the criminal law and I am not persuaded that these difficulties have been overcome in other jurisdictions.'
The decision was welcomed by lawyers who said it would be all but impossible to prosecute someone for such a crime. Doctors said legal action could have driven the disease underground and discouraged those at risk of infection from undergoing HIV tests.
Lawyers said it would be unthinkable for charges to be brought against someone who had infected other people with HIV through sex on the basis of existing legislation. In the 19th century, in the only known case of its kind, a court had decided that a man could not be prosecuted for transmitting venereal disease.
However, people could still be charged if, for instance, they jabbed an infected needle into another person, lawyers said.
Last night, Roy Cornes, a Birmingham man who has admitted having unprotected sex with several women despite being HIV positive, said: 'Kenneth Clarke has got it wrong. I believe it should be a criminal offence to deliberately infect people with HIV.
'The important word is deliberately. I did not do that. When I was diagnosed HIV positive I was not counselled about the dangers.
'I was very young and the doctors did not explain it to me properly. Anyone who now goes around having unprotected sex, knowing they could be passing on HIV, should be dealt with by the law.'