The law on rape which sees just 4% of reported cases end in conviction will be radically overhauled to give a clear definition of "consent" for the first time under reforms published today.

The biggest shake-up in sexual offences legislation would also create a crime of sending sexually offensive e-mails and texts, punishable by up to 10 years in jail, and the extension of the definition of rape to include attacks on men.

The Scottish Law Commission has spent three years working to clarify the current laws which have led to a number of controversial court cases. These include the acquittal of Edward Watt despite his alleged victim repeatedly saying no and the ordeal of 17-year-old Lindsay Armstrong who was raped and later committed suicide after a harrowing cross-examination in court.

The commission hopes including a definition of consent in the statute-books will offer more protection to victims and improve Scotland's rape conviction rate, presently the lowest in Europe.

Consent will be defined as "free agreement" between adults. Crucially, juries will be able to draw on a range of specific scenarios which outline where consent has not been given. These include when a woman is too intoxicated through drink and drugs, is threatened with violence or is deceived about what is happening.

At the moment, the prosecution has to prove the attacker knew his victim did not consent, leading to women being challenged in court about their behaviour leading up to the attack.

Professor Gerry Maher, QC, of the Scottish Law Commission, said: "What we are offering is clarity on what consent actually is. At present, consent is the core part of the definition of rape, but consent itself was never defined. That is the paradox.

"It may be that the jury bring in their own ideas about consent, so what we have done here is to bring in a detailed model of consent. We hope that by offering a legal definition of consent, it may help to change social attitudes towards it."

The proposals aim to bring the sex laws in Scotland into the 21st century. The commission has largely adopted the thinking behind legislation in Victoria, Australia. Sandy Brindley, national co-ordinator of Rape Crisis Scotland, said: "What we have to make sure is that the law surrounding rape and other sexual offences is clear.

"But law reform on its own just isn't enough. While we support principles of sexual autonomy which are central to the commission's reforms, we have to make sure that there is an educational element to them, and that people understand them."

The report has 62 recommendations and will be passed to the Scottish Government, which has proposed to introduce a Bill on rape and sexual offences in 2008.

The new laws would outline a range of sexual coercion offences, which includes legislation on sending e-mails and texts which are of a sexual nature. The sender could face up to 10 years in prison if it can be proved they sent the electronic message to gain sexual gratification, or in order to cause distress or alarm to the person who received it.

The offence of male rape would also be created under the reforms. Professor Maher said: "The existing crime of rape is defined too narrowly. The crime of rape should cover both male and female victims."

The commission has also recommended creating the offence of sexual assault. The offence will carry a maximum life sentence.