A study of 22 raped men, carried out by Prof King in 1989, found that those attacked were of a wide range of ages, with the oldest man assaulted being 84. "Age and sexual attractiveness were often irrelevant, as in the case of women," said the professor.
Male rape was first recognised as a problem in the 1980s and became a crime in law last year. The lack of recognition has helped to perpetuate many myths, such as that it is a crime exclusively committed by homosexuals on other homosexuals, or that a "real man" should be able to fight off a rapist.
Speaking at a conference at De Montfort University, Leicester, Prof King said: "Stranger rape is seen as the norm, but the majority of men know the people attacking them. It's interesting that it's the same for men as for women. Men find it difficult to believe that they can be held down and raped ... that one-on-one men can be intimidated and can't always fight their attacker off."
Survivors, a London-based male rape helpline, estimates that there is a 50-50 split in their callers between homosexuals and heterosexuals.
Prof King said attacks were much more likely to take place in the victim's or assailant's home, a theory backed up by Metropolitan Police figures.
Double the number of men in the year up to 31 March have been raped in a flat as were attacked in a street, and three times as many men had been raped in a flat as in a park.
For both men and women, the most likely age to be raped was 20 to 24, according to the police. Prof King said male victims suffered as much psychological trauma as women who had been raped. His study found the effects on men were devastating. Many as a result developed a phobic avoidance of going out or of other men, suffered severe depression or turned to substance abuse.
A spokesman for Survivors said it was not uncommon for men to wait 20 years after the assault before telling anyone.
Bill Grahamslaw, a Detective Superintendent with the Metropolitan Police, said strenuous efforts had been made by the police to encourage men to report crimes. Male chaperons - trained officers who support and accompany the victim through police procedures - were introduced in 1991.
"The system could work even better," said Det Supt Grahamslaw. "We are undertaking a comprehensive review of the chaperon service so that we are better at meeting the victim's needs.
"We need to encourage more male victims to come forward and make them realise they don't have to go to court. We just want to know that the offence has taken place, so that we can get a better understanding of the issue."