Being drunk or high on drugs may rule out sex, under reforms to the law being considered by the government.

Sex crime reform is set to redefine consent in rape cases if the victim was drunk or high on drugs.

The move could enshrine a "drunk means no" policy in legislation and see a huge rise in the number of "date rape" cases coming before the courts.

In a bid to drive up rape convictions, Home Office ministers are considering moves to scrap a rape suspect's defence of "honest belief" that a victim had given his or her consent to sex if he or she was under the influence.

An official report published two years ago - "Setting the boundaries" - made the case for change.

"A defence of honest belief in free agreement should not be available if there was self-induced intoxication, recklessness as to consent, or if the accused did not take all reasonable steps in the circumstances to ascertain free agreement at the time," said the report.

But critics of the new approach believe the reform could lead to a rise in malicious allegations and cause confusion among late-night revellers.

"It is important that people see rape as something that is not only about a stranger attacking you," said Home Office sources.

"This why we set up the sex offences review and we intend to bring forward legislation to provide root and branch reform on sex offences."

The Conservatives have signalled that they may oppose the move.

Shadow home secretary, Oliver Letwin, will be watching to make sure the government gets it right in proposals set to be featured in the Queen's Speech.

"Clearly the right result is a proper balance of protection in which women are protected against having sex forced upon them and men are protected against malicious claims," he said.

"We shall want to look carefully at the government's proposals to ensure that they achieve that balance."

Other measures to be included in a new Sex Offences Bill are the scrapping of indecency laws that discriminate against homosexuals.

Laws to be withdrawn include those which make it illegal for men to have sex in public places - a practice known as cottaging.

Some Tories have criticised the plans, saying they will make public parks and lavatories "no-go" areas for young heterosexual men.