Conviction rates for sexual offences fell further last year than any other crime, official figures have revealed.
The proportion of prosecuted sexual offences which led to an offender pleading or being found guilty fell in 2013 from 61% to 55%, Ministry of Justice data shows.
Conviction rates for all offences dropped from 83% to 82.1% as all categories, such as violence against the person and robbery, registered falls - but convictions for sexual offences experienced the most significant decrease.
Police and prosecutors have come under pressure in recent months over the success of a number of sexual offence investigations, including Operation Yewtree, the Scotland Yard inquiry launched in the wake of the Jimmy Savile scandal.
There were 10,365 sexual offences proceeded against last year, 988 more than the 9,377 in 2012, the figures showed.
Despite that increase, 5,659 were found guilty in 2013, 69 fewer than the year before.
In addition, 1,349 cautions were issued for sexual offences last year, a drop of 82 from 1,431 in 2012.
Shadow home secretary Yvette Cooper said: " It is alarming that convictions for sex offences are falling at a time when the number of recorded offences is rising sharply.
"We have warned David Cameron and Theresa May for some time that there is a growing justice gap and more serious criminals are getting away with the their crimes without facing prosecution or the courts - let alone conviction.
"Overall, convictions have fallen for sexual offences, domestic violence cases and child abuse cases since 2010.
"It's time the Home Secretary took action to make sure victims get the justice they deserve."
Peter Cuthbertson, director of criminal justice campaigners, the Centre for Crime Prevention, said: "Conviction rates can fall for a number of reasons, including more cases brought to court.
"It is right to bring serious cases to trial even if the chance of conviction may be low. The key is to ensure tough sentencing for those offenders who are found guilty in order to protect the public."
Director of Public Prosecutions Alison Saunders and Martin Hewitt, Association of Chief Police Officers lead for adult sex offences, said earlier this month that j uries should be given advice about the common misconceptions of rape at the start of trials to help avoid confusion.
The two experts are heading a task force to investigate the fall in numbers of successful rape prosecutions and what can be done to reverse the trend.
Common misconceptions can lead to juries deciding rape has not occurred if a victim was drunk at the time or had previously consensual relations with the perpetrator, or basing their views on a victim's sexual history, they said.
Leaving such advice to the end, when a judge is summing up a case, is too late, the pair added, as juries often make up their minds during the course of a trial.
Commenting on the MoJ figures, a Crown Prosecution Service spokeswoman said: " The effective prosecution of rape continues to be a key priority for the CPS.
"The CPS and Acpo have been working together for many months to investigate the reasons behind the drop in the number of rape cases referred by police to CPS, as identified in the last CPS report on violence against women and girls, published July 2013.
"As part of this longstanding piece of work, a meeting was held between police and prosecutors in September and a joint national rape scrutiny panel was convened in April to analyse the drop in referrals.
"A joint CPS/police action plan resulting from this ongoing work on referral rates, but looking at all aspects of prosecuting rape cases from investigations to prosecutions and trials, will be published shortly.
"It will set out a number of actions for police and prosecutors to improve the way these cases are handled. The specific actions will be announced in due course."
Adam Pemberton, assistant chief executive of independent charity Victim Support, said: "It takes great courage for victims of sexual offences to come forward and speak up about their experiences when seeking justice.
"Although each case must be judged on its individual merits, it is startling to see that conviction rates are falling, despite the increase of victims coming forward and bringing alleged offenders to court.
"It's critical that victims are not put off coming forward by these statistics and that they are aware of the support services available to them through our Witness Service before during and after the trial."