The government and police will promise on Wednesday to take action to improve the low rate of conviction for rape, saying more will be done to help victims.

Currently less than six percent of all reported rapes result in a conviction, and while one in 20 women say they have experienced rape, just 15 percent have reported incidents to police.

"Rape is one of the most serious and devastating crimes. We know that it remains under-reported and we are determined to improve this and increase conviction rates," Home Office minister Vernon Coaker will tell a police conference.

The government has been working to provide specially trained police officers, teams of experts and prosecutors across the country, said Coaker. The focus now was on ensuring that the same procedures were followed by every force.

"Every force has a responsibility to ensure that every single officer who comes into contact with a rape victim is supportive and believes the victim," he said.

The pledge comes days after equality group the Fawcett Society obtained figures which showed that there was a "postcode lottery" for rape victims.

It found that in some areas women who reported a rape were almost five times less likely to achieve a conviction than in others, with conviction rates dropping dramatically in some parts of the country.

"It is a national scandal that thousands of victims have no access to justice and receive unreliable and ineffectual responses when reporting rape," said Katherine Rake, the society's Director.

"In many cases women face a culture of disbelief and, even more frequently, delayed responses lead to the loss of vital evidence."

Metropolitan Police Assistant Commissioner John Yates said police had made "significant advances" in the way rape was investigated but admitted more needed to be done.

"Rape is a uniquely difficult crime to investigate," said Yates, who is the Association of Chief Police Officers' spokesman on the issue.

"But the fact that it's difficult means we need to up our game and redouble our efforts to ensure victims can have confidence in the way they are approached by those working in the criminal justice system."

Last week a confidential survey found that three members of the Welsh Assembly had been raped but had not reported the incidents.

Meanwhile last year Conservative leader David Cameron called for rape laws to be tightened to reverse the decline in convictions, saying too many men thought they could "get away" with rape.