The conviction rate for sex crimes has dropped by 10% in a year with thousands more prosecutions failing to produce significantly more guilty verdicts, official figures show.
Despite more than 5,000 extra prosecutions in the year ending June compared to the previous year, only 77 more sex offenders were convicted, leading to accusations that criminals are "getting away with it".
The Ministry of Justice (MoJ) figures showed a fall in the conviction rate for sex offences to 58%, compared to 68% in the year ending June 2013.
Charity Victim Support said victims of sex crimes can feel devastated if their abuser is not convicted and called for action across the criminal justice system to address the problem.
Meanwhile, Labour claimed more offenders were getting away with their crimes and blamed Government cuts to police officers and specialist prosecutors for a failure to deal with complex sex crimes.
The figures show there were 34,161 sex offence prosecutions in the year ending June 2014, with 19,685 resulting in a conviction.
But a similar number of sex offenders - 19,608 - were convicted in the year ending June 2013, despite only 28,809 prosecutions, more than 5,000 fewer.
In contrast the conviction rate for every other serious crime apart from robbery increased or remained the same over the same period.
The release of the figures in the MoJ's quarterly criminal justice statistics comes as the prosecution and conviction of sexual offenders remains high on the political agenda after a string of high profile cases.
Shadow home secretary Yvette Cooper said the Government should establish national standards on the prosecution of sex crimes.
She said: "These figures show the Government is failing to get justice for victims of sexual attacks and abuse.
"More sex offenders are getting away with it, and fewer victims are getting the justice and protection they need.
"The scale of cuts to police officers and specialist prosecutors under Theresa May means they are struggling to cope with complex crimes.
"And the lack of proper national standards means victims are being let down.
"It's the same damaging trend in domestic violence and rape, where fewer victims are getting the justice they deserve and more perpetrators are getting away with it.
"Theresa May needs to face up to the consequences of her policies, take urgent action to increase prosecutions and stop ignoring the growing justice gap."
Adam Pemberton, assistant chief executive of the charity Victim Support, said: "We know from supporting many thousands of victims of sexual offences that after getting up the courage to come forward to testify, they can feel devastated if their case ends without a guilty verdict.
"Successful convictions are often dependent on victims and witnesses being able to give their best possible evidence to the court.
"Victim Support is on hand to provide them with the help and support they need.
"Agencies across the criminal justice system must address this drop in conviction rates, not least as sexual offences have some of the lowest conviction rates compared to other crimes."