New sex crime laws have come into force in the most radical reform of sex offences in a century.
Internet grooming will become a criminal offence
The Sexual Offences Act tightens anti-child sex abuse measures and repeals bans on buggery between men.
Home Secretary David Blunkett said the new act replaces laws which were "based on the Victorian era".
Anyone convicted of contacting a child with the intention of committing
a sex offence will face up to 10 years in jail under a new grooming offence.
Mr Blunkett said: "New laws offer increased protection, especially to children and vulnerable people, combat modern crimes such as grooming and, for the first time, do away with discrimination by applying the law equally to men and women."
A rapist will have to be "honest and reasonable" in their belief they took reasonable steps to ensure their partner consented to sex.
This aims to ensure ministers increase the rape conviction rate, which stands at just 7%.
Juries will be able to assume there was no consent if a rape victim was asleep, unconscious or disabled, or if there was violence or threats involved.
Under the act, men who have previously been convicted of buggery and indecency between men with a consensual partner aged over 16, will have their names removed from the sex offenders' register.
Association of Chief Police Officers spokesman John Yates said: "We have lobbied hard for many of the significant changes, particularly around the re-definition of the offence of rape and for the first time clear legal guidance
around the definition of 'consent'.
"These are dreadful crimes and the challenge for police remains.
"We need to ensure we continue to develop and enhance our response to these crimes at every level, including victim care, forensic recovery and training."
NSPCC Policy Adviser, Christine Atkinson, claimed the new act was "the most significant package of sex offence legislation in many years."
She said: "For too long, child sex offenders have been able to walk away from their crimes with short and insufficient sentences.
"Increasing prison terms to 14 years or in certain cases life, means that at last, sex abusers will feel the full force of the law when they are sentenced."
Measures in the new act include:
Closing a loophole which allowed men to claim sex with under-13s was consensual - any sexual intercourse with a child of that age will be dealt with as rape and carry a maximum sentence of life.
A range of new offences designed to tackle inappropriate sexual activity with children, including a new offence of causing a child to engage in sexual activity which will capture behaviour such as persuading children to undress.
Updating incest offences to cover not just blood relatives but also foster and adoptive parents and live-in partners.
Toughening requirements of the sex offenders' register.
A new offence to protect the public from unacceptable sexual acts in public toilets.
Bestiality and necrophilia become specific offences for the first time.
Voyeurs will face prosecution if they spy on someone else for their sexual gratification.
A new offence of trafficking people for sexual exploitation - with a 14-year maximum term.
Three new offences to protect people with learning disabilities or mental illnesses from abuse.
Definition of rape to include oral and anal penetration.