One of Britain's most senior police officers has called for "an open and honest conversation about rape and sexual offences" as part of a week-long nationwide initiative designed to offset long-standing criticism of police attitudes to the issue.

Deputy assistant commissioner Martin Hewitt, national lead on adult sexual offences for the Association of Chief Police Officers, said that, while victims must be encouraged to report incidents, they also had a right to know the realities of rape prosecutions. It was important that victims be made aware that a third of rape prosecutions do not end with a conviction.

"We need to be honest about the challenges faced in investigating and prosecuting rape," Hewitt said. "Police will do everything they can to ensure that victims get the support they need when reporting a rape or sexual offence. But, despite the bravery and tenacity of the victims who do go through the process, a third of rape prosecutions still don't end in a conviction. That can put people off reporting, because they think it isn't worth it."

Of 3,692 rape prosecutions brought in 2012-13, convictions were reached in 63.2% of cases, a 5.5% increase on 2008-09. Reporting of sexual offences was also up 9% this year, the largest increase since current recording standards began, possibly due in part to historic cases of abuse resurfacing having been triggered by the Jimmy Savile scandal.

"The conviction rate is at an all-time high and this is down to the hard work of police, prosecutors and other agencies to develop victim-focused approaches and take cases through the courts," Hewitt said. "I want to show that victims should have the confidence to report. It triggers a full investigation, but also means victims are able to access medical treatment and support services."

Police forces across the UK will this week run campaigns explaining how they deal with cases of rape and sexual offences, the support victims can expect, and the realities of the judicial process. Hewitt will also be taking to Twitter to answer questions about how the police can better deal with this type of crime.

He will highlight "significant improvements" in the police response to sexual offences: these include specialist training of officers, the introduction of early evidence kits, greater access to sexual assault referral centres, and closer work with support groups.

Jordan Hart, an 18-year-old rape survivor whose attacker was jailed for 11 years, has waived her anonymity to support the campaign and encourage more women and men who are victims of rape to report it. "Reporting to the police gave me peace of mind, knowing I hadn't been beaten by him," she said. "I was supported by my SOIT [Sexual Offence Investigative Techniques] officer, who gave me advice and guidance, and explained what was going to happen and how long it would take; I didn't have to do anything alone."

The director of public prosecutions, Alison Saunders, said she welcomed the debate, which would highlight some of the myths and stereotypes about rape that still influence some members of society: "By continuing to improve the quality of investigations and prosecutions, and ensuring that support to victims is a priority throughout each case, we will encourage others to report these terrible crimes, and further drive up conviction rates."

Hewitt said that there was a need for people to take the debate on prevention of sexual offences seriously. "Most rape involves the coming together of some form of power and some type of vulnerability – either permanent or temporary," he said. "We need to be using all our powers and tactics to understand how this happens, to mitigate the vulnerability, and reduce the opportunities for that power to be abused. I am keen to talk about how this can be done."